Preventive and health promotion work by health visitors ought to reduce social inequalities in child health. However, the increased health and developmental problems among disadvantaged children may constrain health visitors' ability to carry out effective preventive work. This paper measures the impact of socioeconomic inequalities in children's health on the work of health visitors and the amount of preventive work they can provide, with emphasis on 'parenting' programmes. Data collected for health visitors' profiles were analysed in an ecological cross-sectional study. Individual caseloads were classified according to the proportions of families in social class IV or V and families headed by an unemployed person. A range of measures of young children's health and development indicated the demands on health visitors' time. Preventive work was divided into post-natal support, parenting programmes, special clinics and other preventive work. All the outcome measures were poorer in the most disadvantaged caseloads. Odds ratios between the most and least disadvantaged 20 per cent of caseloads were 0.6 for breast feeding at birth, and at seven months, 1.9 for post-natal depression, 3.2 for mothers under 18, 10 for lone parent families, 2.6 for families needing high intervention, 4.5 for families with a smoker, 11 for domestic violence, 4.4 for parents with a chronic health problem, 2.7 for children on the child protection register and 2.8 for children with developmental problems. There was 30 per cent greater health visitor time provided in the most disadvantaged caseloads than in the most advantaged. There was no consistent difference in the amount of preventive work carried out; in particular, parenting programmes were delivered at a similar rate in all caseloads. Large differences in demands on health visitors' time exist between affluent and disadvantaged caseloads which are barely reflected in the provision of extra time to poorer caseloads. There is no consistent pattern to the delivery of preventive programmes designed to ameliorate the effects of disadvantage on children's health and development.