An analysis of the HLA-types of 351 children in whom a diagnosis of insulin dependent diabetes mellitus (IDDM) had been made between 1960 and 1990 revealed that although the frequencies of HLA-DR3, -DR4, -DR3/4, -B8 and -Bw62 were increased there was, depending on the year of diagnosis, a marked fluctuation in the frequencies of these HLA-antigens and in the frequency with which -B8 was associated with -DR3 and -Bw62 with -DR4 suggesting heterogeneity/variation in agents initiating/triggering IDDM.