To evaluate the therapeutic possibilities of chronic electrical stimulation, muscle function studies and quantitative tests of physical assessment were used to monitor the response of quadriceps femoris to prolonged low frequency stimulation. Comparative studies of the maximum voluntary and electrically elicited responses of muscles of young ambulant children with Duchenne muscular dystrophy, when compared to those of normal children's muscles, revealed lower values of maximum voluntary contraction, significant slowing (P less than 0.001) of mean relaxation times and a higher resistance to fatigue testing. Intermittent chronic low frequency stimulation resulted in a significant (P less than 0.01) increase in mean maximum voluntary contraction of the stimulated muscles compared with the mean force exerted by the unstimulated control muscles. There are clear therapeutic possibilities for the use of chronic low frequency stimulation in these children.