The effects of an orally administered Cassia occidentalis extract were studied in chickens. A 25 mM sodium bicarbonate solution effectively extracted the toxic principle. Toxic activity was reduced, but not eliminated, when the heated extract (90 C, 40 minutes) was administered. The toxic principle was in the pellet after centrifuging the extract at 38,000 X g. Daily administration of the extract produced weight loss and muscular weakness. Microscopic examination revealed skeletal and cardiac muscle degeneration and hepatocyte vacuolation. Electron microscopic examination revealed mitochondrial disruption. Respiratory studies on liver mitochondria isolated from treated chickens demonstrated lower phosphorylation ratios, lower respiratory control ratios, and lower rates of oxygen use.