HLA phenotype distribution was investigated in 91 affective patients. Significant increases over those of the control population were found in HLA-A 29 and in Bw 22 frequencies, while A 10 and A 30 were decreased. No significant difference was shown between the two clinical subgroups (41 unipolar patients and 50 bipolar ones). On comparing our data with those from other authors, Bw 16 was significantly increased. However, a high degree of heterogeneity was also shown for this antigen. Of some interest is the finding that relapsed and non-relapsed patients during long-term lithium therapy display diverging HLA phenotype distributions, with B 5 increased among the non-relapsed subjects.