Between October 1988 and December 1990, 60 patients with leukaemia (25 with AML, 19 ALL and 16 CML) undergoing BMT were randomised in a double-blind clinical trial to receive prostaglandin E2 (PGE) (Prostin E2, 0.5 mg per tablet) or placebo for prophylaxis of oral mucositis. Patients had to dissolve tablets in the mouth three times daily starting 7 days before BMT and continuing until 21 days after BMT. The incidence of severe oral mucositis was similar for both groups, 55% in patients receiving PGE and 52% in patients receiving placebo. The duration of severe mucositis did not differ between PGE and placebo groups (chi-square 0.95, p = NS). The incidence of HSV infection was significantly higher in patients receiving PGE. Patients with HSV infection receiving PGE also had a higher incidence of severe oral mucositis. The results presented indicate that PGE is not effective for prophylaxis of oral mucositis in BMT recipients.