To test the hypothesis that intrauterine insemination with washed spermatozoa induces antisperm antibody formation, we measured serum antisperm antibody levels by the Immunobead technique in a population of women receiving exogenous gonadotropins. Antibody levels were measured before therapy (baseline) and then serially during subsequent stimulation cycles, for a maximum of six cycles. Twenty-eight patients underwent intrauterine insemination; each patient served as her own control. An additional 25 patients were treated with exogenous gonadotropins but did not undergo intrauterine insemination; they served as external controls. Antisperm antibody levels in women who underwent concomitant intrauterine insemination were compared with levels in those who did not. Of the 53 enrolled patients, 18 completed six treatment cycles, and 35 achieved pregnancy before six cycles. Forty-five patients (85%) had less than 10% Immunobead binding, six (11%) had binding between 10% and 25% (mean 16%, range 14% to 20%), and two had binding greater than 25% (28% and 42%, respectively). Mean binding was similar (less than 10%) in the intrauterine insemination and external control groups. Eighteen patients conceived in the intrauterine insemination group and seventeen in the control group. Of patients who conceived, all but one had less than 10% Immunobead binding at the time of conception (mean 1.6 months). In patients who did not conceive, there was no difference in Immunobead binding between control and intrauterine insemination groups after 6 months of therapy. Our data do not support the hypothesis that serum antisperm antibody levels, as detected by Immunobead binding, will increase in menotropin-stimulated women undergoing intrauterine insemination over a prolonged treatment period.