Sildenafil (Viagra) is readily available over the internet without the need to consult a doctor or a pharmacist, according to researchers from the University of Pennsylvania.They conducted a search of the world wide web and identified 77 sites which offered to deliver sildenafil without a visit to a doctor. Of these sites, 55 per cent provided information about contraindications for sildenafil and only 42 per cent gave instructions for use. Many sites did not require information about the consumer's medical history and only 35 per cent specified that a doctor would review each questionnaire. Fifty-seven per cent asked about nitrate use and 52 per cent requested information about diagnoses of angina or coronary heart disease. Only 5 per cent of sites asked customers to verify that they were male.The authors conclude that the purchase of pharmaceutical agents over the internet may increase the risks of adverse effects and the inappropriate use of medication (New England Journal of Medicine 1999;341:1389).