Rehabilitation of patients with osteoarthritis of the knees is typically based on home exercise. These programs are believed to benefit patients and have been shown to qualitatively improve strength. The purpose of the present study was to quantify the effects of a 3-mo home exercise program on muscle function and functional capacity. The progressive program included flexibility, strength, endurance, active range of motion and functional activities. Nineteen subjects (67.4 +/- 7.5 yr) with osteoarthritis of the knees began the program, with only nine completing it. The subjects initially had significantly reduced muscle function and functional capacity. Maximal isometric strength of knee extension increased significantly at a knee flexion position of 45 degrees for hip flexion positions of 120 degrees and 60 degrees (35%); however, it failed to increase at longer muscle lengths. There were no significant improvements in hamstring strength. Maximal angular velocity improved after 3 mo of exercise (40%). Muscle endurance did not improve significantly. Although there was a slight increase in functional capacity, these data failed to demonstrate significant clinical or statistical improvement in overall function in patients after home exercise.