Recurrent urinary tract infections are known to occur among 5 per cent of all females. These women frequently have episodes of symptoms of lower urinary tract infection even between periods of bacteriuria. In the present study, 25 women with a history of recurrent urinary tract infections, found to lack signs of obstructive uropathy, were subjected to an extensive urological and microbiological survey. The investigation showed that (i) "pyuria" was common (9/12) but usually of urethral origin, (ii) introital and/or urethral colonization with Enterobacteriaceae often (11/25) occurred, (iii) apart from Escherichia coli found in three patients, a Bacteroides species was isolated in two and ureaplasmas in one patient from suprapubically aspirated urine, and (iv) chlamydia, gonococci, and trichomonads were not found. The patients were given methenaminehippurate for 1 week and then reexamined. The treatment did not seem to influence the indigenous flora of the lower urogenital tract.