Twenty-nine dogs received renal allografts with simultaneous bilateral nephrectomy. Five recipients were untreated, five were given daily s.c. injections of normal horse serum, 14 received daily injections of horse anti-dog antilymphocytic serum (ALS) at varying intervals before and after transplantation, and five were treated with daily injections of immune globulin prepared from the ALS by sodium sulphate precipitation and diethylaminoethanol cellulose chromatography.The mean survival times of the untreated control animals and those receiving normal horse serum were 9.6 days and 10 days respectively. No animal in these groups survived for more than 12 days.In the ALS-treated dogs, some prolongation of survival was achieved when the serum was started as late as 5 days postoperatively, but the best results were obtained with 5 days' pretreatment and continued postoperative administration, the dogs in this group showing a mean survival of 68.4 days even with a limitation of survival credit to 100 days.Immune globulin admistered on this schedule produced a mean survival of 28 days, so that some immunosuppressive activity was lost in the processing of the serum.