Dogs undergoing renal allografts were treated with phytohemagglutinin‐M (PHA‐M) with and without azathioprine before and after transplantation. PHA‐M treatment was associated with histological evidence of decreased renal allograft rejection and minimal azotemia. PHA‐M‐treated animals had marked leukocytosis postoperatively and, unlike untreated control animals or azathioprine‐treated dogs, had sustained elevations in total lymphocyte levels. However, PHA‐M treatment did not decrease survival due to associated drug toxicity manifested by a distemper‐like syndrome not observed in other concurrently evaluated animals.