The aims of the present investigation were (a) to evaluate the effect of eccentric quadriceps training in patients with unilateral patellofemoral pain and (b) to compare the effect of eccentric and concentric quadriceps training in patients with bilateral patellofemoral pain. Fifteen patients (9 male and 6 female, aged 17-36 years with a mean of 27.5 years) participated in this study. Nine patients had unilateral pain and trained their painful leg eccentrically, while six had bilateral pain and trained one leg eccentrically and the other concentrically. Quadriceps muscle training was performed on a Kin-Com dynamometer at 90 degrees/s and 120 degrees/s angular velocity twice a week for 8 weeks. Before and after the treatment period the thigh muscle torques were measured on the Kin-Com dynamometer at 60 degrees/s, 90 degrees/s, 120 degrees/s and 180 degrees/s for quadriceps and at 60 degrees/s and 180 degrees/s for hamstrings. Nine controls, matched for gender and age with the group with unilateral pain, were tested in the same way on the Kin-Com dynamometer. For functional evaluation a knee score was calculated before training, after 8 weeks of training and at a mean of 3.4 years after completion of the training. After 8 weeks of training and at follow-up times of 1 and 3.4 years the patients were also questioned regarding whether or not they felt improvement from the training programme. To determine the degree of knee pain during the training Borg's pain scale was used. The results showed that, compared with the controls, the patients had a significantly lower knee extensor torque in their painful leg at all velocities measured.(ABSTRACT TRUNCATED AT 250 WORDS)