A spermicidal agent called "741" is used in the People's Republic of China as a substitute for nonoxynol-9 in vaginal contraceptive preparations. The relative spermicidal activity of these two agents was evaluated using dog, rabbit, monkey and human semen. Acute LD50 determinations in mice were also performed. The spermicidal activity and acute toxicity of both agents were either identical or very similar in all species. Since agent 741 is less expensive than nonoxynol-9 to manufacture and equally as potent in vitro, it is an alternative spermicide for vaginal contraceptive formulations.