Seventeen newly diagnosed type 1 diabetics were studied longitudinally--at diagnosis, after 5 months and after 2 years, for antibodies against the following viruses: Coxsackie B3, B4 and B5, Echo 11, and Adeno 7a. The latter two were chosen because they had been isolated frequently in the area during the year the patients were diagnosed, whereas the Coxsackie viruses previously have been associated with the aetiology of type 1 diabetes. Coxsackie B4 antibody titres fell from the diagnosis and the 5 month study to the 2 year study (p less than 0.02), and, at this time, the average titre was also lower than in 37 healthy control individuals (p less than 0.05). Over the same period Coxsackie B3 antibody titres increased (p less than 0.05). Echo 11 antibody titres were higher in the patients at diagnosis (p less than 0.05), but, otherwise, no significant titre differences, compared with controls or titre changes, were found at any of the study times. Patients with lower suppressor cell activity at diagnosis displayed higher mean antibody titres regarding the five viruses together, than did patients with higher suppressor cell activity (p less than 0.05). No significant correlations were found between, on the one hand, the antibody titres and, on the other hand, C-peptide values, insulin dosage, degree of glycaemic control, or specific tissue type, HLA-B8 or HLA-DR3 and/or 4.