This paper presents the results of a method to produce autonomous animation of virtual humans. In particular, the proposed methodology is focused on the autonomous synthesis of nonvoluntary gestures such as reflexes and subtle movements which provide a noticeable impression of realism and naturalness. The final goal of this technique is to produce virtual humans with a more spontaneous, non preprogrammed behaviour. For the moment, the technique is applied to the synthesis of reflex movements of the arm, in reaction to thermic stimuli. Nevertheless, a general architecture is outlined