A controlled trial of behaviour modification in the treatment of sleep problems is described. The subjects were 51 children aged 4 months to 4 1/2 years (mean 20 months) recruited from the community by health visitors (specialist nurses based in the community). In the experimental procedure health visitors were trained and supported in the use of behaviour modification. At 6 months follow-up both control and experimental groups showed equally marked improvement. Reasons for the failure to demonstrate an effect are discussed.