HLA, A, B and C antigens were determined in 84 South African Indian patients with non-insulin-dependent diabetes mellitus (NIDDM) in whom age of onset was under 35 years and in 760 healthy Indian controls. Increased frequencies of Aw24, B15 and Bw61 were seen in the patients, but the corrected P value was not significant. Among Indians of North Indian origin, however, there was a significant association between B15 and NIDDM (corrected P less than 0,012; relative risk 4,8). In Indians of South Indian origin no clear association with any specific HLA antigens was seen, although there was a slight increase in the frequency of Aw24 (uncorrected P less than 0,007; corrected P greater than 0,05). The findings in this study serve to emphasize the heterogeneity of diabetes mellitus, since no association between NIDDM and HLA antigens has been noted in whites.