The effects of repetitive contractions of the isolated levator ani muscle of the immature male rat were investigated on glucose uptake, the accumulation of D-xylose-14C, and α-aminoisobutyric acid-14C (AIB-14C) as well as on the incorporation of leucine-3H, proline-3H and valine-14C into protein and adenine-14C into RNA. These effects were compared with the effects of insulin. Glucose uptake and D-xylose-14C accumulation were increased during the period of contractions and after this period for at least three hours. Insulin and contractions had additive effects on these uptakes. AIB-14C accumulation was also stimulated by contraction. This effect increased with the incubation time and was maximal at a frequency of 60 imp/min. The effect lasted for at least three hours after the period of contractions. The stimulating effect of insulin on AIB-14C accumulation in the muscle was reduced by contractions. A reduction was also obtained on the incorporation of normal amino acids into protein as well as on the incorporation of adenine-14C into RNA. The stimulating effect of insulin on the rate of incorporation of amino acids into protein was reduced during the contraction period. No insulin-like activity could be found in the media of contracting muscles, when these media were tested with fresh muscles for effects on the accumulation of AIB-14C or D-xylose-14C.