The left thumbs and great toes of three 8 1/2 month old Rhesus monkeys (Macaca mulatta) were amputated in guillotine fashion one millimeter distal to the base of the nail and allowed to heal by the conservative open wound method. Healing occurred in seven to ten days in these small digits. Each of the thumbs and toes grew back with some blunting and shortening of the digit tips, but were functional. The new structures were cosmetically pleasing as in the human instances. The nails grew essentially to normal size and shape supported by the remaining portions of the distal phalanges. Histological studies showed no evidence of blastema formation such as is observed in the regenerating limb of the Urodele (newt) taken as the comparative representative. The possibility of improving the regrowth is discussed against the background of our knowledge of the importance of nerve during limb regeneration in lower vertebrates.

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