Heat-labile enterotoxin (LT) was purified from an enterotoxigenic Escherichia coli 015H11 of human origin. The purification steps included French pressure cell disruption of the bacteria, salting-out, DEAE-Sephacel on chromatography. Application of this procedure resulted in a 95.1-fold purification of LT with a yield of 19.9% as determined by rabbit ileal loop assay. The final LT preparation showed only one protein-staining band on polyacrylamide gel electrophoresis, indicating that the purified LT was homogeneous.