This paper presents basic considerations on the design of small lightweight motors intended primarily for actuating robotic and prosthetic hands. New actuators, compact enough to be incorporated in the links of articulated hands, have the potential for significantly improving hand dexterity by reducing the control complexity, friction and backlash intrinsically associated with present tendon-based actuation techniques. In order to develop motor units for actuating the joints of a three-link anthropomorphic finger developed in our laboratory, we have investigated the technology of shape memory alloys (SMAS). The SMA actuator consists of two motor modules working in push-pull mode and located inside the structure of the proximal finger phalanx. The design and mechanical performance of each module are presented. Experimental results indicate that SMAS, despite some control problems originating from the intrinsic complexity of their thermoelastic behaviour, can be effectively used for the intended goal.