One hundred and seven unrelated Danish patients considered to be manic-depressive according to strict diagnostic, symptomatic and course criteria were typed for antigens of the HLA system, the major histocompatibility system in man. Preliminary results from the first 47 patients had previously been reported to suggest a positive association between manic-depressive disorders and HLA-A3, HLA-B7, and HLA-Bw16 and a negative association between such disorders and HLA-B8. Results from the extended series provide confirmatory evidence that there is a positive association between manic-depressive disorders and HLA-Bw16 and also strongly suggest a positive association between HLA-B7 and such disorders. HLA typing may prove to be a useful way of identifying sub-groups of manic-depressive patients for other biological studies. The associations described provide a potential lead for formulating hypotheses about the nature of the biological mechanisms which predispose to manic-depressive disorders.