Nine patients who had undergone resection of various well defined parts of the triceps surae muscle because of tumour were examined. The function was estimated from the patient's history and the muscle strength was measured statically and dynamically using a Cybex II dynamometer. Two patients reported slight symptoms. The loss of strength was less than one might expect from theoretical calculations. The strength of the operated limb showed a particular pattern depending on the part resected. From this pattern it was concluded that the soleus is more active when the foot is dorsiflexed and the gastrocnemius more active when the foot is in plantar flexion, and that the gastrocnemius is most important in quick movements of the foot.