The electromyographic responses elicited in the first dorsal interosseus muscle by small muscle stretches or by electrical stimulation of the median nerve were investigated in parkinsonian patients and in age-matched healthy subjects. Stimuli were applied during a steady level of contraction in the intrinsic hand muscle. This ensured comparable levels of excitability in the alpha-motoneurone pool in patients and normals. It was found that the normal short-latency stretch reflex was almost absent in rigid patients, while responses to electrical stimulation of low-threshold nerve fibres were of equal size in both groups. This result suggests that there is a change in fusimotor control of muscle spindles in Parkinson's rigidity without alteration of the central gain of the Ia-transmitted stretch reflex.