Summary when 12 normal preschool children and 12 mentally handicapped children of similar mental age were individually observed during peer group play, more similarities than differences were found in the incidence of 28 behaviours. However, the behaviours for which significant differences were found included those likely to be most relevant to social acceptance. Mutual social involvement of normal and handicapped children during integrated play may require not only attention to the constitution of the groups but also manipulation of the conditions and environment.