A treadmill apparatus was used for estimating the recovery of locomotor activity after dopaminergic grafts to rats with unilateral 6-OHDA lesions in the nigrostriatal DAergic pathway. Naive control rats, 6-OHDA lesioned rats, and grafted rats were trained to run on the uphill treadmill for 20 min per day for 7 successive days. Weak electrostimulation (ES), less than 1 mA, was used to force running, ie, if rats did not run they received ES from the grids fixed behind the treadmill belt. The numbers of ES that the rats received were counted because they reflected the frequency with which the rats failed to meet the treadmill speed. Control rats received 5-10 ES/10 min on the first day but only 0-1 ES after the second day. Lesioned rats and grafted rats received over 100 and 50-100 ES/10 min, respectively, during the first 3 days. Thereafter, lesioned rats still received frequent ES (80-100/10 min), whereas grafted rats received less (20-30/10 min). Results indicate that motor ability in grafted rats may not be ameliorated completely despite the recovery from drug-induced rotations. This treadmill running test was found to be a useful method for quantitative evaluation of motor ability.