1. 1. Muscle fiber composition of antennal muscles of the rock lobster Palinurus vulgaris, was studied. Three fiber types (fast, slow and intermediate) were recognized within extensor and flexor muscles of the distal joint, on the basis of histochemical stainings for NADH diaphorase and ATPase. 2. 2. A correlation between oxidative capacity of a muscle fiber, as measured by NADH diaphorase activity, and myofibrillar ATPase activity was shown to exist. 3. 3. The spatial distribution of fiber types was analysed in muscle cross-section and a regional distribution of the fiber types was demonstrated within both antagonist muscles. 4. 4. The functional significance of the results is discussed in relation to the contractile performances of the muscles and to the behavioural role of the rock lobster antennae.