This study evaluated weekly urine cultures of patients with neurogenic bladder disease who underwent intermittent urinary catheterization for bladder retraining. One group of 53 patients in 1974 received regular instillations of 0.1% neomycin after each catheterization. A similar group of 55 patients in 1975 did not receive neomycin and constituted a control group. Distribution of age, sex, diagnosis, and duration of bladder retraining was comparable in both groups. Quantitative bacterial colony counts of 10 4 to 10 5 or greater per ml of urine were considered significant. There was no difference in the incidence of bacteriuria between the neomycin-treated group and the control group (53 versus 49%, respectively), and most patients in each group had colony counts >10 5 /ml. Escherichia coli was seen less frequently in neomycin-treated patients (43.4 versus 62.5%), but a greater percentage of infections due to Pseudomonas aeruginosa , group D streptococci, and yeasts was noted in the neomycin-treated group than in the control group (41.5 versus 22.5%).