Objective To determine the efficacy of treating semen specimens with platelet -activating factor (PAF) before IUI. Design Prospective randomized double-blin ded study of PAF treatment of sperm for patients with a history of infertility u ndergoing IUI. Setting Private infertility center. Intervention(s) Patients had ovulation induction therapy with clomiphene citrate (CC)-or gonadotropin, two I UIs per month with PAF treatment. Main outcome measure(s) Clinical pregnancy rat es. Result( s) There was a significant difference in IUI pregnancy rates per cyc le between control (10/56; 17.9%) and PAF (14/47; 29.8%) treatment groups in t he normal male study arm. There was a significant difference in cumulative IUI p regnancy rates between control (10/35; 28.6%) and PAF (14/26; 53.9%) patient g roups in the normal male study arm. There was no significant difference in IUI p regnancy rates per cycle between control (12/124; 9.7%) and PAF (14/119; 11.8% ) treatment groups in the male factor study arm. There was no significant differ ence in cumulative IUI pregnancy rates between control (12/46; 26.1%) and PAF ( 14/38; 36.8%) patient groups in the male factor study arm. There was a signific ant difference in overall cumulative IUI pregnancy rates between control (21/81; 25.9%) and PAF (27/64; 42.2%) patient groups. Conclusion( s) The inclusion of PAF into the IUI spermwash procedure significantly improves pregnancy rates. Ho wever, the signifi-cant improvement can only be shown to affect men presenting with normal semen parameters. Objective To determine the efficacy of treating semen specimens with platelet-activating factor (PAF) before IUI. Design Prospective randomized double-blin ded study of PAF treatment of sperm for patients with a history of infertility udergoing IUI. Setting Private infertility center. Intervention (s) Patients had ovulation induction therapy with clomiphene citrate (CC) -or gonadotropin, two I UIs per month with PAF treatment. Main outcome measure (s) Clinical pregnancy rat es. Result (s) There was a significant difference in IUI pregnancy Rates per cyc le between control (10/56; 17.9%) and PAF (14/47; 29.8%) treatment groups in t he normal male study arm. There was a significant difference in cumulative IUI p regnancy rates between control (10 / There was no significant difference in IUI p regnancy rates per cycle between control (12/124; 9.7%) and PAF (14/26; 53.9%) patient g roups in the normal male study arm. 14/119; 11.8%) treatment groups in the male factor stu There was no significant differnce in cumulative IUI pregnancy rates between control (12/46; 26.1%) and PAF (14/38; 36.8%) patient groups in the male factor study arm. There was a significant ant difference in The cumulative of IUI pregnancy rates between control (21/81; 25.9%) and PAF (27/64; 42.2%) patient groups. Conclusion (s) The inclusion of PAF into the IUI spermwash procedure significantly improves pregnancy rates. Ho wever, the signifi-cant improvement can only be shown to affect men presented with normal semen parameters.