Our purpose was to characterize in the rhesus monkey the structure and function of vascularized temporalis muscle flaps innervated by the facial nerve after translocation into the site of the denervated zygomaticus muscle. Animals were killed at 28 to 120 days following translocation. Control data were obtained from the contralateral side. Twenty-eight days after translocation, the time to reach peak twitch tension and one-half relaxation time were 170% of control zygomaticus muscle. Contraction times decreased with time and reached control values by 100 days. Absolute isometric tetanic tension was not different between the flap (4.29 +/- 1.28 newtons; X +/- SEM) and control zygomaticus (3.95 +/- 0.80 newtons). Succinate oxidase activity of the flap decreased from 279 +/- 18 nl O2/mg protein/min to control zygomaticus values (98 +/- 18) by 110 days. The type 1 fiber cross-sectional area of the flap was 52% of control temporalis muscle and 150% of control zygomaticus muscle (P less than 0.05). The temporalis flap demonstrated viable structure and function and appeared useful in facial movements.