A prospective study was carried out in 103/863 obstetric patients with cystitis characterized by urinary urgency and frequency, dysuria, pyuria and suprapubic discomfort in the absence of systemic symptoms such as fever and costovertebral angle tenderness. The association of symptomatic lower urinary tract infection with low-count bacteriuria (10(2)-10(5) UFC/mL of urine) was present in all the patients. The incidence of cystourethritis was about 12%, most of the infections occurred at the first trimester. To learn whether a multiple-dose of nitrofurantoin or ampicillin is safe and effective therapy for acute uncomplicated urinary tract infections, 103 symptomatic pregnant women were randomly grouped to receive oral nitrofurantoin (100 mg t.i.d.) or ampicillin (500 mg t.i.d.) for five days. Seventeen patient were excluded since they did not return for follow-up. Escherichia coli was isolated in 67% of infections. Overall cure varied from 87% to 89%, without any great differences between the regimens. Nine patients had asymptomatic bacteriuria in the course of pregnancy, four developed acute pyelonephritis and one of them had abnormal intravenous pyelogram.