The effects of antigenic competition between ovalbumin and sperm autoantigens have been studied in guinea pigs. There was an inhibition of antiovalbumin antibody production up to 60 days after immunization. The cell-mediated immunity against ovalbumin was also depressed at day 30. The simultaneous immunization with both antigens has no effect upon the humoral and cell-mediated immunity against spermatozoa. During the period of inhibition of the humoral and cell-mediated antiovalbumin response, the number of animals developing autoimmune aspermatogenic orchitis was diminished compared to those immunized with spermatozoa alone. Later on, there was no difference between the two groups. The transient inhibition of the immune response against ovalbumin can be explained by the particulate nature of the autoantigens. The sperm cells may be easily trapped by the dendritic reticular cells of the draining lymph nodes. This in turn could affect T cell recognition at early stages, orienting it predominantly toward the sperm autoantigens. At day 90 the situation returned to that present in animals immunized with ovalbumin alone.