Non-therapeutic research in children is said to be justified in part if the risk involved is no more than minimal, but there is little information on the risk of venepuncture to make that judgement. This prospective study was carried out to assess the effect of venepuncture on 425 healthy children aged between 3.6 and 6.6 years old who participated in a non-therapeutic research project. A parental questionnaire was sent out 1 month after the blood was taken. Three hundred and ninety-one parents (92%) returned the questionnaires. Parental responses indicated the risk of complications was of the order considered to be minimal. A large majority of parents (78%) felt this experience would be helpful for the child if blood had to be taken again and a significant proportion (40%) felt the child would be more confident when going to see a doctor or dentist afterwards. Venepuncture in preschool children causes minimal harm and might even have some positive effects.