Thirty-one women with the recurrent urethral syndrome (abacterial cystitis) had extensive microbiological, cytological and histological investigations. A Streptococcus species was isolated from the bladder aspirate of one patient, a wall-deficient Streptococcus species from two others and both a Lactobacillus species and Ureaplasma urealyticum from another. A possible microbiological cause was therefore identified in the bladder in only 4 of the 31 patients. A Lactobacillus species was isolated from the bladder aspirate of one control subject. Lactobacilli were grown in the voided urine of the majority of patients and in seven of the eight control subjects. Chlamydia trachomatis and Herpes simplex were isolated from the cervix and the urethra of one patient. Urethral cytology was normal in all patients. Trigonitis was noted at cystoscopy in 26 of the 31 patients. Bladder biopsies showed squamous metaplasia in 15 and lymphocytic infiltration of the lamina propria in 29, giving support to an inflammatory aetiology of this enigmatic syndrome.