To achieve higher rates of acrosomal loss for in vitro studies of human sperm function, the effect of liposomes prepared from the phospholipid, dilauroylphosphatidylcholine (PC12), on human spermatozoa was investigated. In general, acrosome loss was induced with PC12 with an associated decline in the percentage of motile spermatozoa. Reduction of bovine serum albumin concentration in the incubation medium from 12 mg/mL to 3 mg/mL resulted in a more pronounced effect of PC12, with a significant reduction (P less than 0.001) in the percentage of motile spermatozoa within 1 hour of incubation with PC12. The percentage of spermatozoa observed to be acrosome-free under staining with fluorescein-conjugated Concanavalin A lectin was significantly reduced (P less than 0.05) when spermatozoa were incubated with PC12 (260 mumol/L) in the absence of calcium. The percentage of motile spermatozoa was not different during PC12 incubations when Ca2+ concentration (0, 2.5, and 5 mmol/L) was altered. An active motility pattern was restored in PC12-treated human spermatozoa by subsequent incubation in a defined medium containing 7.5 mmol/L adenosine 5'-triphosphate and 20 mumol/L cyclic adenosine 3', 5'-monophosphate. It was demonstrated that PC12-treated human spermatozoa were capable of binding to the zona pellucida of salt-stored human oocytes once an active motility pattern had been restored.