Current efforts to increase livestock utilization of tarbush have been coupled with studies to examine potential tarbush toxicity. To examine the effects of long term ingestion of tarbush by lambs, 38 (19/treatment) ewe lambs were assigned at birth to receive either tarbush or alfalfa (15%, dry matter basis) in a sorghum-based pelleted creep feed. Lambs were pen-fed this diet 60 days pre-weaning and 60 days post-weaning. No differences existed between treatments in feed consumption. One Iamb died of unknown causes at 90 days of age, while three lambs died between US and 120 days of age. There were no deaths in the alfalfa group. Prior to death lambs appeared lethargic, disoriented and anorectic. At 122 days of age, five Iambs from each treatment were randomly selected from the remaining lambs. Fcces and jugular serum samples were obtained from these animals before necropsy the following day. All fecal samples were negative for occult blood. Serum creatine kinase (P < .05), gamma glutamyl-transfcrase (P < .01), aspartate aminotransfcrase (P < .01), lactate dehydrogenase(P < .01) and total cholesterol (P < 0.5) concentrations were elevated in lambs fed tarbush, while conjugated bilirubin concentrations and platelet counts tended (P < 0.1) to be elevated. Histologic examinations revealed myopathic lesions and diffuse apoptotic liver necrosis in lambs fed tarbush. Interestingly, four out of five lambs fed alfalfa had renal and urinary calculi, while calculi were not found in lambs fed tarbush. These data indicate tarbush will cause muscle and liver damage, with possible secondary cholcstasis when fed for extended periods of time.