Low dosage intravenous (< 0.01 micrograms.kg-1.min-1) and oral prostaglandin E have been reported to produce fewer complications than higher intravenous doses in the ductal manipulation of congenital heart disease. Over a 3-year period 34 patients were treated with low dosage intravenous or oral prostaglandin. Eighteen (53%) had complications associated with this treatment with 14 having more than one complication. Major complications occurred in nine neonates: necrotising enterocolitis (7), apnoea/bradycardia (5), convulsions (1), haemorrhage (1), and resulted in a change of management. This study therefore concludes that the high incidence of complications is similar with both low and high dosages of intravenous and oral prostaglandin. The use of prostaglandin in any form deserves caution.