Efficiency of immunization of splenocytes in vitro by three kinds of prostate antigen has been studied. Intact cells of the human prostate cell line LNCaP, a membrane preparation (PMA) of LNCaP cells, and prostate specific antigen (PSA) were used as antigens. Three different schemes of in vitro immunization were tested: male spleen cells vs female; single donor spleen cells vs. mixed lymphocyte culture (MLC); addition of exogenous IL-2 vs. no lymphokine addition. The supernatant antibodies were tested for reactivity to the immunizing antigen by ELISA. Subsequently hybridomas were generated by fusing the primed lymphocytes to a heteromyeloma cell line, K6H6/B5. Only antigen specific IgM responses could be detected. Intact LNCaP cells induced the highest responses from mixed lymphocyte cultures. PMA also induced the highest responses from mixed lymphocyte cultures of male origin, whereas both single donor and mixed donor spleen cell cultures of female origin responded to PMA. However, anti-PMA responses by mixed lymphocyte cultures of female cells were significantly augmented by addition of IL-2. PSA only induced specific responses from mixed female splenocyte cultures supported with IL-2. Several anti-PMA and -PSA antibodies were generated after somatic fusion of the in vitro primed cells. Two monoclonal IgG antibodies from LNCaP primed spleen cells could be competitively inhibited with tumor membrane antigen.