Therapy of urinary tract infections with nitrofurantoin macro-crystals. The aim of this study is to evaluate the therapeutic effectiveness of two dosages of nitrofurantoin macro-crystals. Between January 1993 and February 1994, 101 patients (54 male and 47 female), either suffering from urinary tract infections or on whom internal examination had been carried out, were treated with nitrofurantoin macro-crystals. There were divided into two groups: A, a posology of 100 mg 3 times daily for 7 days and B, a posology of 100 mg 4 times daily for 7 days. A urine culture was carried out on all patients before and after treatment. E. Coli was found in 60.5% of cases, Streptococcus Faecalis in 12.7% and Staphylococcus aureus in 5.6%. Infection was eliminated in 85.3% of patients in group A and 93.9% in group B. The dysuric symptomatology was cured in 84.6% of patients in group A, and 89% in group B. The statistic elaboration of the results with X2 and p tests did not reveal any difference between the two groups examined.