Guinea pigs were immunized with sperm antigen(s) in complete or incomplete Freund’s adjuvant. Those immunized with sperm in CFA developed orchids, made high titers of complement fixing antibody; their lymphocytes could transfer orchitis when inoculated into normal recipients and produced in vitro migration inhibitory factors. Those immunized with sperm in ICFA did not develop orchitis and made high titers of anaphylactic antibodies; their lymphocytes did not transfer orchitis into normal guinea pigs and did not inhibit migration of macrophages. Lymphocytes from guinea pigs immunized with CFA could transfer orchitis when inoculated into the testes of guinea pigs immunized with ICFA. Hence the lack of disease in guinea pigs immunized with ICFA is not because of a protection of their testes by non-phlogogenic antibodies.