Rats immunized with a semipurified preparation of the Escherichia coli heat-stable (ST) enterotoxin conjugated with a protein carrier were protected against challenge with semipurified or purified ST and viable organisms of multiple heterologous serotypes that produce only ST (LT-/ST+), but they were not protected against heal-labile (LT) toxin or viable strains which produce LT either alone (LT+/ST-) or together with ST (LT+/ST+).
