We studied the distribution of HLA-D--related (DRw) antigens in 40 patients with juvenile diabetes mellitus (JDM) and 79 matched controls. We found that DRw2 was significantly decreased in the JDM group, suggesting a protective effect of the antigen and that the decrease observed in B7 was secondary. HLA-DRw3 and HLA-DRw4 were increased in the diabetic group, and, as with B8/B15, these two antigen predisposed to the disease additively. The susceptibility for JDM was found to be more strongly related to HLA-DRw3 that to B8. On the other hand, B15 rather than DRw4 showed the stronger association with JDM. Moreover, we found that this second diabetogenic gene is associated primarily with B15 and only secondarily with Cw3, which is in linkage disequilibrium with B15. This study further emphasizes the immunogenetic heterogeneity of JDM.