A newborn infant developed systemic herpes simplex infection. Skin vesicles appeared on the 4th day. The diagnosis was confirmed on the 13th day and intravenous idoxuridine started. A total of 580 mg./kg. was given over 5 days, with clinical evidence of improvement. A relapse occurred at 23 days and the baby died aged 28 days. The postmortem findings are described. Further trial of idoxuridine in neonatal systemic herpes simplex is suggested.