Two healthy females and twelve healthy males, aged 19-24 yr, underwent strength training for periods of 9-21 wk. The muscles trained included extensor digitorum brevis (N = 3), soleus (N = 7), brachioradialis (N = 4), and the hypothenar muscles (N = 3). The effect of training on motoneuron excitability was measured as the degree to which two reflex responses (V1 and V2) were potentiated by voluntary effort. Strength training was found to increase V1 and V2 potentiation by 49.7 and 38.9%, respectively, (P less than 0.01) for pooled muscle comparisons with the exception of the soleus V2 wave, which was rarely seen and excluded from this analysis. There was a positive correlation (r = 0.83, P less than 0.01) between the change in the V1 and V2 potentiation. It was argued that strength training may cause an increased ability to raise motoneuron excitability during voluntary effort.