Eight different mimic muscles of 13 human cadavers (7 male, 6 female) were studied by histochemical techniques. In sections stained for myosin ATPase the composition of fibre types was quantitatively evaluated by computer-assisted image analysis. The data were compared to those of 2 muscles in the lower limb of the same individuals. According to the percentage of the type I muscle fibres 3 groups of mimic muscles were distinguished: (1) the orbicularis oculi muscle (15%), (2) the major zygomatic, levator labii superioris, levator anguli oris, depressor anguli oris muscles and platysma (27-38%), and (3) the occipitofrontal and buccinator muscles (57-77%). For comparison, the gracilis and rectus femoris muscles were built up by 36% and 48% of type I fibres. The average diameters of fibres in mimic muscles were significantly less than in the 2 limb muscles. Differences in muscle fibre size between male and female specimens were not significant. The relevance of morphological characteristics of mimic muscles for facial expression and reconstructive surgery is discussed.