Purified human spermatozoa do not regularly stimulate lymphocytes in spermlymphocyte cultures (SLC). This lack of consistent stimulation was found not to be dependent on sperm/lymphocyte ratio or on culture peak response time. A few weak stimulations obtained are not HLA-D or sex dependent. Contaminating seminal cells other than spermatozoa (SC non-SZ) may be responsible for the high stimulations found in SLC by others, since, in our hands, purified suspensions of SC non-SZ stimulate allogeneic lymphocytes in an HLA-D-dependent fashion, and such responses are abrogated by anti-HLA-DR monoclonal antibodies. These functional data confirm our previous finding of HLA-DR molecules on SC non-SZ by absorptions (and a lack of expression on spermatozoa) and suggest the concomitant expression of HLA-DQ and -DP products.