To evaluate a health education program to improve family management of asthma, 310 children with asthma and their 290 parents were randomly assigned to a program or control group. Program families participated in health education designed to resolve specific management problems and build self-confidence in the ability to manage asthma. Following education, program parents scored better on an asthma self-management index than parents in the control group (+1.57 versus -0.83, P less than 0.0001). Program parents also scored better on two subindices of the self-management index: attack management (+0.87 vs. +0.42, P less than 0.05) and preventive measures (+0.42 vs. -0.35, P less than 0.05). Also, program parents reported significantly more use of guidelines to determine appropriate levels of physical activity for children. Following education, program children reported more use of three management steps than control children: productive cough or postural drainage (59% vs. 35%, P less than 0.004), breathing and relaxation exercises (80% vs. 65%, P less than 0.05), and attempts to stay calm (12% vs. 2%, P less than 0.05). Program children reported significantly less worry than control children about the limitations asthma imposes and about making mistakes at school.