1. Lantana intoxication of guinea-pig caused a decrease in hepatic microsomal protein content, the phospholipid: protein ratio, and the cholesterol: protein ratio. 2. Activities of aniline hydroxylase, aminopyrine N-demethylase, NADH-cytochrome c reductase, NADH-ferricyanide reductase, UDP-glucuronosyl transferase, cytochrome P-450 and glucose 6-phosphatase were decreased. 3. Activities of Mg2+-ATPase and Na+-K+-ATPase were increased. However, activities of 5-nucleotidase and NADPH-cytochrome c reductase were unaffected. 4. The liver endoplasmic reticulum is an important target organelle during lantana poisoning of guinea-pigs.