Abstract : This study was designed to test the hypothesis that: (1) enterotoxigenic E. coli characteristically colonize mammalian small intestine by adhering to the epithelial surface; and (2) that adhesion, referred to above and involving strains lacking K88 antigen, occurs between pili on the bacterial surface and microvilli on villous absorptive cells of the host. This document contains two closely related papers, including 'Immunizaion of Suckling Pigs against Enterotoxigenic Escherichia coli Infection by Vaccinating Dams with Purified Pili'. Pregnant dams vaccinated with purified pili K99 or 987 protected their suckling neonates against lethal challenge by virulent enterotoxigenic E. coli. Protection was dependent upon antigenic homology between vaccine and challenge strains.