Infection is a frequent complication and cause of death in renal failure. Although it is widely accepted that uremia has an adverse effect on host resistance to infectious disease, this association has not been proven. In the present experiments, the relationship between uremia and susceptibility to infection has been investigated using an animal model of chronic, severe uremia. Lung infections (using Pseudomonas aeruginosa and Klebsiella pneumoniae), bacteremia, peritonitis and subcutaneous infection (using Escherichia coli) were induced in uremic and normal rats and the course of infection compared. The ability of the uremic host to clear Ps. aeruginosa from the lung was marginally impaired in the first 24 hr after the challenge but was normal in the later stages of the infection. Similarly, in the bacteremia study, secondary invasion of the lungs by several other species of bacteria occurred in 33% of the uremic animals. We found no other evidence of impairment of immunity in uremia in the infections that we studied and, taken overall, the results support arguments that uremia per se is unlikely to be an important factor predisposing patients with renal failure to infection.