The aim of this study was to analyze in vitro the effect(s) of peritoneal fluid (PF) on sperm motility. Seventy PFs obtained during laparoscopy were tested on motile-rich sperm suspensions. Proportion of motile sperm and velocity distribution were evaluated by multiple-exposure photography technique. At time (t) = 0, PFs increased both sperm parameters as compared with control (P less than 0.01). Maximum effect was observed at t = 5 hours: 32 (45%) PFs increased and 5 (7%) decreased the proportion of motile sperm, while 8 (11%) PFs increased and 4 (6%) decreased sperm velocity. No correlation was found between a particular infertile group and a definite negative effect. However, 70% of PFs from fertile women maintained or increased the proportion of motile sperm at t = 5 hours, compared with 36% in the total infertile group. Comparison of the sperm motility effect(s) of a given PF on different ejaculates revealed that the effects observed also were influenced by the sperm sample tested. In conclusion, PFs can maintain or increase the motility of spermatozoa as function of time. However, some PFs can inhibit sperm motility and these effect(s) can be influenced by the sperm sample.