A Thai woman from Bangkok was admitted to a hospital in Paris for a cholera-like illness. A culture of her "rice-water" diarrhea was negative for Vibrio cholerae and enterotoxigenic Escherichia coli but was positive for Aeromonas sobria. This strain produced enterotoxin, cytolysin, proteolysin, hemolysin, and a cell-rounding factor. Acute -and convalescent-phase sera showed an increase in neutralizing antibodies to enterotoxin, cytolysin, and hemolysin. The enterotoxin, which was labile at 100 C, induced an accumulation of fluid in the rabbit ileal loop model and was not neutralized by antiserum to cholera toxin. Suckling mouse assays and rabbit permeability skin tests were negative, and the Y1 mouse adrenal cell assay produced not true cytotonic effect. This report, the first of an infection due to A. sobria alone, provides evidence that A. sobria is an enteric pathogen of humans that can cause a toxin-mediated, life-threatening illness.