The Today Contraceptive Sponge was evaluated as a vehicle for the delivery of aryl 4-guanidinobenzoates (AGs) which are highly active sperm acrosin inhibitors. Studies in animals have shown that several AGs are more potent vaginal contraceptives and less irritating to the vagina than nonoxynol-9 (N-9), the most frequently used active ingredient in commercial vaginal contraceptive formulations. Neither nonoxynol-9 nor the material that could be solubilized from the sponge matrix altered the enzyme-inhibitory activity of 4'-acetamidophenyl 4-guanidinobenzoate HCl (AGB), 4'-carboxyphenyl 4-guanidinobenzoate HCl (EGB) or 4'-carbomethoxyphenyl 4-guanidinobenzoate HCl (MSGB). Besides being acrosin inhibitors, all three AGs exhibited antimotility activity towards human spermatozoa, EGB being as potent as N-9. The antimotility effects of the AGs and N-9 were additive. For subsequent studies, AGB was used as the model compound. Manufacture of the AGB-containing sponges did not affect the chemical structure of AGB. Good release rates of AGB were obtained from the sponges over a 7-day period. The release rates were 20-50% higher when the sponges also contained N-9. These results indicate that certain AGs exert a dual contraceptive action on spermatozoa by inhibiting both the sperm enzyme acrosin and sperm motility. Furthermore, the polyurethane sponge appears to be a convenient and satisfactory long-term delivery system for the AGs. A mixture of N-9 and AG can be used clinically because these compounds have no adverse effects on each other.