The present investigation was aimed at assessing the difference in peak torque between normal and osteoarthritic (OA) knees in females. Fifty-five female osteoarthritic patients with 85 osteoarthritic knees were studied. Thirty-three normal females of similar age were also collected as a control group. The muscle torque of the knee flexor and extensor was assessed by a Cybex II dynamometer. The speed of isokinetic contraction was set at 30 RPM, 5 RPM, and 0 RPM. The muscle torque of the affected knee in patients with unilateral osteoarthritis was found to be significantly greater than that of those with bilateral osteoarthritis (p less than 0.05). The peak torque of OA patients at the faster speed (30 RPM) showed significant deterioration with age. Compared with the value for controls, the deficit of peak torque in geriatric patients was significant (p less than 0.05), especially at the faster speed (30 RPM). The decrease in extensor torque in OA knees tended to be greater than that of flexor torque, especially in patients less than 51 years of age at 5 RPM and 0 RPM. Age, duration of illness and the grading of X-ray change accounted for isokinetic torque differences in osteoarthritic knees.