A short-term course of an intravenous cephalosporin (cefuroxime) was used as therapy in 24 cases of pyelonephritis due to susceptible organisms in 23 pregnant women. Clinical cure was achieved in 96% of patients, and there were no adverse reactions to the drug. Bacteriologic cure was documented in 52% of those clinical cures, whereas 26% were considered to have bacterial colonization. However, 50% of those patients with bacteriologic cure subsequently had bacteriuria or pyelonephritis caused by other organisms. We conclude that women who have pyelonephritis in pregnancy are at high risk for subsequent urinary tract disease, even if adequately treated for their index infection. Short-term parenteral antibiotic therapy, followed by long-term oral suppressive therapy, is probably the treatment of choice for pyelonephritis complicating pregnancy.