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The in vitro binding properties of enterotoxins of Vibrio cholerae and Escherichia coli to different pure gangliosides and related neutral glycosphin-golipids were analyzed with a sorbent assay utilizing plastic tubes to which the glycolipid substances had been coupled. It was found that the cholera toxin bound to G_M1 ganglioside better than to the other tested substances G_M3, G_M3-NGN, G_M2, G_D1a, G_D1b, G_T, G_A1, tetrahexoside-GlcNac and globoside. With this assay using G_M1-coated tubes it is possible to measure cholera toxin even at concentrations below 1 ng/ml. Also enterotoxin of various E. coli strains bound to G_M1, but the affinity was much less than for cholera toxin. The G_M1 ganglioside, in contrast to the other glycosphingolipids, effectively inactivated cholera toxin as determined with the intradermal and the ileal loop assays; approximately equimolar concentrations of the ganglioside in relation to toxin …