Rauwolfia vomitoria included in the ration of feeder steers at levels of 5, 25 and 125 mg per head per day improved growth and feed efficiency at all levels. Best results were with 25 mg per day. Hydroxyzine fed at levels of 1.25, 2.5, 10, 50 and 500 mg per head per day improved growth and feed efficiency of cattle at all levels with best results at the 1.25 and 10 mg levels. Hydroxyzine included in rations of lambs at levels of .24, 1.2, 6 and 30 g per ton improved growth and feed efficiency with best results at the 1.2 g level. Rauwolfia''vomitoria included at a level of 3 g per ton improved lamb growth to the same extent as hydroxyzine but feed efficiency improvement was somewhat inferior. There was no evidence of depression of carcass grade or dressing percentage from the tranquillizer treatments and there was no indication of sedation of the animals with the levels of tranquilizers fed.