Vaginal contraceptive products have been available for many years and usually contain the membrane surfactant nonoxynol-9 (N-9) as one of the main ingredients.1 However, the major drawback of using N-9 or other surfactants is their detergent-type cytotoxic effect on vaginal cells.2 Besides, N-9 is also known to inactivate lactobacilli, which form the normal flora in the vaginal tissues. Disturbance of the vaginal microflora can lead to vaginal infections which in turn increase the chance of sexually transmitted infections.3 Therefore, development of vaginal contraceptive that lacks membrane toxicity will offer a significant clinical advantage over the currently marketed detergent-type spermicides.4 As an alternative, various other substances blocking or retarding the motility of spermatozoa are being examined to be useful as successful vaginal contraceptive devices, e.g. lysenin, immotilin, nisin and magainin etc. Microorganisms are also known to inhibit sperm motility either directly by agglutinating the spermatozoa or excreting extracellular products that immobilise the sperms. The influence of different uropathogenic microorganisms such as Escherichia coli, Enterococcus, Pseudomonas aeruginosa, Staphylococcus saprophyticus, Candida albicans on human sperm motility has been studied in vitro by Huwe et al.5 Yin et al.6 showed that at high concentrations, Streptococcus viridans could induce sperm agglutination in vitro. Jiang and Lu7 reported that Staphylococcus aureus significantly immobilises the spermatozoa. In an earlier work performed in our laboratory, we have also isolated a sperm-agglutinating factor (SAF) from S. aureus, which agglutinates human and other mammalian spermatozoa.8 Further, in the present study, the efficacy of SAF as a contraceptive agent has been investigated.