Oral administration of lantana leaf powder to guinea pigs caused a decrease in hepatic and renal tissue dry weight, DNA and protein contents. Total carbohydrate content decreased in liver but was not affected in the kidneys. RNA content (as a ratio of tissue dry weight) showed an increase in both liver and kidneys. Lipid content of liver tissue increased while it decreased in the kidneys. Relative amounts of protein, DNA and RNA showed significant alterations in both the tissues.