A three part investigation of the factors that might influence uptake of immunisation was carried out in Maidstone Health Authority; this included studies of the computer system and attitudes of parents and professionals. Several problems with immunisation scheduling, information transfer between general practitioners and clinics and the computer centre, and validity of computer information were identified. The attitudes of parents, relatives, and friends were generally favourable, although parents reported a lack of knowledge about the disease and vaccine and lack of advice from professionals. Perceived contraindications to immunisation, particularly a history of measles, were important reasons for non-uptake. Professionals' perceptions of contraindications, however, were at variance with Department of Health and Social Security guidelines and none of the recorded contraindications was valid. Calculations of potential uptake suggest that a 90% target uptake is feasible and recommendations are made for changes in services.