Physiological studies have been made of extensor digitorum brevis muscles in 28 healthy subjects aged between 60 and 96. Within this elderly population there was evidence of muscle wasting and weakness. These changes were shown to result from a loss of functioning motor units. The surviving motor units were often enlarged and tended to have relatively slow twitches. In some subjects the maximum impulse conduction velocities were reduced in motor nerves; there was evidence that slowing of impulse conduction could be especially marked in distal regions of axons. The findings are considered to indicate the presence of motoneurone dysfunction in old age.