Fifty-three patients with recurrent genital herpes were subjected to a double-blind trial with topically applied idoxuridine in dimethyl suiphoxide and dimethyl suiphoxide alone as control.Lesions treated with 20% idoxuridine healed more rapidly and shed virus for a shorter period than those treated with 5% idoxuridine or the controls. Five per cent idoxuridine however was superior to the control.Thirty-four of the patients were followed up for periods up to 2 years but no significant difference in the recurrence rate of the lesions was observed between those treated with idoxuridine and the controls.