Background. Urinary tract infections (UTIs) are very common and have been treated with apparent success with antimicrobials for many years. However, there is a paucity of placebo-controlled clinical trials. Aim. To measure the symptomatic and bacteriological short-term nitrofurantoin treatment versus placebo, in the treatment of uncomplicated UTI in adult non-pregnant women. Design of study: Randomised placebo-controlled in general practice. Setting: Non-pregnant women, aged between 15 and 54 years old consultancy a general practitioner for symptoms suggestive of uncomplicated lower UTI and with pyuria (positive for leucocyte esterase test). Method: A dipslide was inoculated in first-void midstream urine and sent for examination. The patients were randomised to receive nitrafurantoin 100 mg or placebo four times daily for three days. After three, seven, and 14 days a new dipslide was inoculated and symptoms of UTI were checked for the disappearance or improvement of symptoms and bacteriuria. Results: Of 166 women consulting with symptoms suggestive for UTI, 78 had pyuria and agreed to participate in the study (the clinically suspected UTI group); of these, 40 received nitrofurantoin and 38 received placebo. The result for combined symptomatic improve nitrofurantoin and cure after three days was 27/35 in the nitrofurantoin group and 19/35 in the placebo group (c(2) with Yates' correction P = 0.08; number needed to treat [NNT] = 4.4, 95% confidence interval [CI] = 2.3 to 79). After seven days, combined improvement and cure was observed in 30/34 and 17/33 respective 7 (P = 0 003, NNT = 2.7, 95% CI = 1.8 to 6.0). At inclusion, 56 women had bacteriuria of greater than or equal to 10(5) CFU/ml (the bacteriologically proven UTI group). Of these, 29 received nitrofurantoin and 27 received placebo. After three days the bacteriological cure was 21/26 in the treatment group, compared with 5/25 in the placebo group (P < 0.001; NNT = 1.6, 95% CI = 1.2 to 2.6). After seven days the bacteriological cure rate was 17/23 in the intervention group and 9122 in the placebo group (P = 0 05 NNT = 3 95961 G = 1.7 to 17). Conclusion: in women with bacteriologically proven UTI, nitrofurantoin was significantly more effective than placebo in achieving bacteriological cure and symptomatic relief in just three days, this was still present after seven days. In patients with clinically suspect was statistically significant after there was a trend towards significance.