31 patients with a urinary infection were treated with a single oral dose (3 g for adults and 100 mg/kg for children) of amoxycillin; 23 (74%) were cured. 20 women and 26 children were then randomly allocated to either a single dose of amoxycillin of a 5- to 7-day conventional course of the same antibiotic. The results of both treatment regimens were comparable. Single-dose therapy for the treatment of urinary-tract infections was simple, effective and well tolerated. Patients preferred taking their treatment in this manner. Failure of single-dose therapy to eradicate bacteriuria may indicate which patients require subsequent investigations of their urinary tract.