An antibacterial agent, taurolin, formed by the combination of 2 molecules of taurine with 3 molecules of formaldehyde has been tested against anaerobes in vitro and in vivo. In vitro, taurolin is highly active against Bacteroides species and anaerobic Streptococci as measured by the minimum inhibitory concentration. In vivo, small dosages of taurolin given intraperitoneally increase the mortality in mice with Bacteroides peritonitis. However, by increasing the dosage of taurolin, survival is prolonged and mortality reduced. Intravenously administered taurolin protects rabbits from the effects of Bacteroides fragilis infection whether the organisms are given intravenously or intraperitoneally.