The effect of Lactinex, a lactobacillus-containing pharmaceutical, on rabbit ileal loop reactions induced by enterotoxigenic Escherichia coli was studied. Lactinex granules, tablets, or its separate components were mixed and incubated in vitro with toxigenic E. coli prior to injection into ileal loops. Since inocula were free of preformed enterotoxin, reactions indicated in vivo enterotoxin production. Lactinex granules reduced loop fluid when compared with that induced by the positive control (P<0.001) or inocular containing Lactinex tablets (P=0.009). Whey powder, 109 and 107Lactobacillus acidophilus, and 108Lactobacillus bulgaricus were the only Lactinex components that significantly reduced loop fluid. © 1979, Springer-Verlag New York Inc.. All rights reserved.