Nitrofurazone-coated urinary catheter segments inhibited 51 (75%) of 70 urinary bacterial isolates from patients with indwelling catheters. Inhibition zones correlated significantly with the nitrofurazone MIC (r2 = 0.79, P = 0.0001). All strains except the Pseudomonas spp. were inhibited by < or = 64 micrograms of nitrofurazone per ml. MICs of nitrofurazone and nitrofurantoin correlated significantly (r2 = 0.93, P = 0.0001).