Preliminary results of a study of the extent to which training health visitors in behavior modification techniques improves the effectiveness of their work with families of young children are presented. A total of 14 health visitors were recruited and assigned to training and delay-of-training groups. Selected from case loads, participating 3-year-old children were nominated by the health visitors as those likely to benefit from behavioral management intervention and those scoring high on a behavioral checklist which had been completed by their mothers. Three main comparisons were made: matched cases from trained and control group health visitors, intervention and non-intervention cases within the trained group, and all the families assessed from the caseload of trained and control health visitors. Reported findings concern (1) changes in mothers' responses on the past helpfulness of the health visitor, (2) changes in the total number of spontaneously mentioned problems, (3) changes in the Behavioural Screening Questionnaire Score, (4) mother's and father's irritability with the child, (5) fear of loss of self-control with the child, and (6) incidence of striking the child. The direction of the effects and those approaching or reaching significance all indicate greater change being associated with training. Tentative indications support the view that sleeping or eating problems are more likely to respond to health visitor intervention than more confrontational behavior problems. Four pages of references and five tables are provided. (RH)