Synthetic Biologics Reports First Quarter 2012 Financial Results -- Preclinical and Clinical Programs Moving Forward -- For Immediate Release Ann Arbor, MI

Synthetic Biologics Reports First Quarter

2012 Financial Results

-- Preclinical and Clinical

Programs Moving Forward --

Ann Arbor, MI, May 15, 2012 -

Synthetic Biologics, Inc. (NYSE Amex: SYN), a developer of synthetic DNA-based therapeutics and innovative disease-modifying

medicines for serious illnesses, today reported financial results for the three months ended March 31, 2012 and summarized operational

Operational Highlights

Management Team - Strengthened

Clinical Development and Regulatory Affairs Functions

Synthetic Biologics - Focus on

DNA-Based Therapeutics

Multiple Sclerosis (MS) - Two

Phase II Clinical Trials Ongoing

Board of Directors - Improved

Corporate Governance

"We continue to focus our efforts

on establishing our presence in the field of next generation' gene therapy and on advancing our strong mid-to-late

stage clinical programs," said Jeffrey Riley, Chief Executive Officer of Synthetic Biologics. "We've strengthened

our management team, improved our corporate governance practices and maintained a cash position consistent with current needs."

Three Months Ended March 31, 2012 Financial Results

As part of management's plan to

streamline our focus, we sold the clinical reference lab on March 8, 2012. Laboratory revenues for the three months ended March

31, 2012 and March 31, 2011 were charged to discontinued operations, resulting in no revenues for these periods. In addition,

the gain on the sale of the clinical reference lab of $677,000 was included in discontinued operations for the three months ended

General and administrative expenses increased

by 19% to $1.5 million for the three months ended March 31, 2012, compared to $1.2 million for the same period in 2011. This change

is primarily the result of increased salary and consulting fees associated with strengthening our senior management team and expanding

our emphasis on investor outreach. Non-cash charges related to stock-based compensation decreased to $499,000 for the three months

ended March 31, 2012, from $759,000 for the same period in 2011.

Research and development expenses were

$386,000 for the three months ended March 31, 2012, compared to $231,000 for the same period in 2011. This 67% increase is primarily

driven by the expansion of our pipeline, including the initiation of our preclinical program for the treatment of PAH and our

clinical trial for the treatment of cognitive dysfunction in MS.

Other income, net, was $5,000 for the

three months ended March 31, 2012. Other expense, net, was $759,000 for the three months ended March 31, 2011, and included a

$810,000 charge related to the estimated fair value of the warrants associated with the January 2011 financing adjusted for the

change in their fair value at the end of the period, offset by other income of $63,000 related to the settlement of accounts payable

previously accrued in prior periods.

Cash at March 31, 2012 was $6.8 million

compared to $6.7 million at December 31, 2011. As of April 30, 2012, we had approximately $6.5 million in cash.

About Synthetic Biologics, Inc.

Synthetic Biologics is a biotechnology

company focused on the development of synthetic DNA-based therapeutics and innovative disease-modifying medicines for serious

illnesses. Synthetic Biologics is developing, or has partnered the development of, product candidates for the treatment of pulmonary

arterial hypertension (PAH), relapsing-remitting multiple sclerosis (MS), cognitive dysfunction in MS, fibromyalgia and amyotrophic

lateral sclerosis (ALS). For more information, please visit Synthetic Biologics' website at www.syntheticbiologics.com.

UltraVector and RheoSwitch Therapeutic

System are registered trademarks of Intrexon Corporation.

This release includes forward-looking

statements on Synthetic Biologics' current expectations and projections about future events. In some cases forward-looking

statements can be identified by terminology such as "may," "should," "potential," "continue,"

"expects," "anticipates," "intends," "plans," "believes," "estimates,"

and similar expressions. These statements are based upon current beliefs, expectations and assumptions and are subject to a number

of risks and uncertainties, many of which are difficult to predict and include statements regarding our continued focus of our

efforts in the field of gene therapy and advancing our clinical programs and the expected size of the future market for sales

of oral disease-modifying therapies for MS. The forward-looking statements are subject to risks and uncertainties that could cause

actual results to differ materially from those set forth or implied by any forward-looking statements. Important factors that

could cause actual results to differ materially from those reflected in Synthetic Biologics' forward-looking statements

include, among others, a failure to receive the necessary regulatory approvals for commercialization of our therapeutics, a failure

of our clinical trials to be commenced or completed on time or to achieve desired results, a failure of our clinical trials to

receive anticipated funding, a failure of gene therapy to receive market acceptance, or a failure by us or our strategic partners

to successfully commercialize products and other factors described in Synthetic Biologics' report on Form 10-K/A for the

year ended December 31, 2011 and any other filings with the SEC. The information in this release is provided only as of the date

of this release, and Synthetic Biologics undertakes no obligation to update any forward-looking statements contained in this release

on account of new information, future events, or otherwise, except as required by law.

- Financial Tables to Follow -

For further information, please contact:

Vice President of Corporate Communication

(734) 332-7800, Ext. 22