This study examined the effects of ankle and wrist weights on acute physiologic responses during treadmill running. Eight physically active young men completed eight running tests at their predetermined "most comfortable" speeds with zero, 1.6, 3.2, and 4.8 kg of additional weight equally distributed on the ankles or wrists. Energy expenditure and heart rate increased as a linear function of the additional weight placed at both anatomic locations. The magnitudes of these responses were significantly higher with the weights at the ankles than at the wrists, and were independent of the strength and endurance of the pertinent muscle groups involved in overcoming the additional weight. Blood lactate concentrations tended to increase during the loaded runs. However, the values were not significantly different from those observed during control (zero load) runs. Perceived exertion increased significantly over the control value when the heaviest weights were placed at the ankles and wrists. Since ankle and wrist weights increase training intensity and energy expenditure during treadmill running, they may result in greater increases in cardiovascular fitness and greater weight loss than would be realized by training without their use.