The hair root pattern in full-thickness skin autografts in guinea pigs was evaluated on the basis of findings in a total of 34 grafts. Between the 4th and 12th day after surgery the proportion of anagen hairs was found elevated and increasing in all cases. Thus spontaneous loss of hair was not preceded by transformation of anagen hairs into telogen hairs. New hair growth did not occur until 3 to 4 weeks after surgery, and was succeeded by several accelerated synchronous hair growth cycles. This is interpreted as a result of secondary hypoxic damage to the hair follicles due to congestive hyperemia in the subepidermal vascular plexus, as described elsewhere.