Protection against acute pyelonephritis was induced by immunization of baboons with purified P-fimbriae of Escherichia coli as vaccines. To test for cross-protective capacity of two different P-fimbriae vaccines we vaccinated baboons with P-fimbriae purified from either E. coli strain ER2 or strain JR1 and subsequently challenged the animals with E. coli strain JR1. All vaccinated animals showed elevated antibody titers to P-fimbriae from both of the E. coli strains used. Both vaccines tended to reduce the time of bacteriuria. They partially prevented pyelonephritis and protected against loss of renal function.