Thirty out-patients with chronic recurrent urinary tract infections, who had failed to respond to 10 days treatment with either pivmecillinam and/or amoxycillin, received a 3-month course of pivmecillinam at a dose of 200 mg, three times daily. Twenty-seven patients had bacteriuria due to Enterobacteriaceae, mainly Escherichia coli, sensitive to mecillinam in vitro. Pivmecillinam eradicated all the initial urinary pathogens. Reinfections occurred during treatment in three patients, who remained asymptomatic. Four subjects complained of gastro-intestinal side-effects, and therapy was withdrawn in three instances. Another three patients described unusual adverse events towards the end of the course of treatment, described as an odd sensation in the body and a desire for salt. The sensation disappeared a few days after the end of treatment. Treatment with pivmecillinam had no adverse effect on haematopoietic, hepatic or renal function.