BANGOR – Two more former executives of a Winslow biological laboratory pleaded guilty Thursday to their role in a scheme to smuggle a chicken virus into the country from Saudi Arabia in order to produce a vaccine.

John Donahoe, 59, of Flowery Branch, Ga., and Dennis Guerrette, 40, of Brunswick pleaded guilty in U.S. District Court in Bangor. Both men are free on bail.

It is illegal to import avian influenza into the United States even for research purposes.

Donahoe, a veterinarian, was president of Maine Biological Laboratories before he resigned in the spring of 2001. Guerrette was the company’s vice president and chief financial officer. He left the firm in September 2002.

The two pleaded guilty Thursday to counts including conspiracy, mail fraud and other federal charges, all in connection with the scheme. In his first appearance before U.S. District Court Judge John Woodcock, Donahoe waived indictment and pleaded guilty.

Guerrette pleaded not guilty in January to a five-count indictment, but on Thursday changed his plea on three of the charges. Guerrette pleaded guilty to conspiracy to commit mail fraud and two counts of mail fraud. A third count of mail fraud and being accessory after the fact of smuggling are still pending.

A jury trial in Guerrette’s case had been scheduled to begin next week.

A sentence hearing for the two is expected to be held later this year.

Donahoe faces more than seven years in prison and more than $375,000 in fines. Guerrette faces up to 10 years in prison and more than $500,000 in fines. Both also may be required to pay restitution to the company for the losses it incurred because of the scheme.

Four others also have been charged in the scheme.

Thomas Swieczkowski, the company’s former vice president of production, and Marjorie Evans, former vice president of quality assurance and regulatory affairs, have pleaded guilty to similar charges. Their sentencing dates have not been set.

Earlier this year, former lab workers Walter Gogan, 63, of Winslow and Peggy Lancaster, 47, of Mount Vernon each were sentenced to two years probation for their part in the cover-up.

The case dates to 1998, when a Maine Biological customer in Saudi Arabia discovered one of its chicken flocks had avian influenza, according to the indictment. To produce a vaccine, Maine Biological required a sample of the virus, which was then smuggled into the United States, according to prosecutors.

After producing a vaccine, company officials allegedly falsified production records and shipping documents to send it to the Saudi customer.

The Associated Press contributed to this report.