Using an indirect lymphokine-assay, the leucocyte-migration-inhibition-test (LMI-test), the cellular sensitization of fertile and infertile patients before and after homologous and heterologous intrauterine insemination (IUI) was investigated. In this assay several preparations of spermatozoa ("washed"-, "swim-up"- and "pellet"-spermatozoa) in different concentrations (1, 5 and 10 x 10(6) sperms/ml culture medium) and seminal plasma were tested as antigen. In all investigated groups a cellular immune response against spermatic antigen was demonstrable and seemed to be dose dependent. In contrast to fertile women who reacted with an enhancement of the macrophage migration for low concentrations the same concentration of antigen induced an inhibition of macrophage migration in fertile patients. For high concentrations of spermatic antigens there was a difference in the intensity of cell-mediated immune response between fertile and infertile women. Since infertile patients demonstrated an increased level of cell-mediated immune response it is possible that infertility may be caused by this altered immunological reaction. This response changes after multiple IUI-treatment and that change might be caused by the high concentration of spermatic antigens as there was a difference in the intensity of cell-mediated immune response between fertile and infertile women. Since infertile patients demonstrated an increased level of cell-mediated immune response it is possible that infertility may be caused by this altered immunological reaction. This response changes after multiple IUI-treatment and that change might be caused by the high concentration of spermatozoa. The immunological response of infertile patients seems to be similar in those receiving husband and donor IUI.