In order to investigate a possible viral aetiology for Type 1 diabetes the polymerase chain reaction (PCR) technique was used. Pancreatic tissue from Type 1 diabetic subjects was examined for the presence of a panel of common viruses. Primers specific for mumps, measles, cytomegalovirus, and Epstein Barr virus, as well as primers located in a highly conserved region of the enterovirus genome which are capable of detecting all of the following family members: Coxsackie B, echovirus, polio, mengovirus, and encephalomyocarditis virus were used to screen 18 Type 1 diabetic subjects of whom 3 had proven insulitis, 12 Type 2 diabetic subjects and 18 non-diabetic controls. Epstein Barr virus was detected in two Type 1 (13%), two Type 2 (22%), and three of the normal nondiabetic pancreases (20%), and the DNA sequences confirmed by direct sequencing. Cytomegalovirus was detected in one of the normal pancreases only and no evidence of any of the other viruses was found. It is concluded that the Type 1 diabetic pancreatic samples studied did not show persistence of infection with any of the above viruses. Non-persistent acute infection of the pancreas by the above viruses cannot be excluded in the aetiology of Type 1 diabetes from this study.