Effect of low-dose continuous treatment with FK506 on the development of GVHD. Histology of target organs from an animal treated with FK506 at 1.0 mg/kg followed by 0.1 mg/kg/q.o.d. (group 7). Biopsies of (A) ear, (B) tongue, (C) liver, and (D) small bowel were taken 60 days after BMTx. There was no histological evidence of GVHD, except for foci of lymphocytic exocytosis, seen in the tongue.