Oral administration of lantana leaf powder to guinea pigs caused an increase in the hepatic postmitochondrial fraction:homogenate ratios of activities of lysosomal enzymes--acid phosphatase, cathepsin B and DNase II. Enzyme activities of glucokinase, aldolase, lactate dehydrogenase and glucose-6-phosphate dehydrogenase were elevated whereas activity of glutathione-S-transferase decreased. Alterations in the activities of lysosomal and cytosol enzymes appear to constitute an important biochemical lesion in the pathogenesis of guinea pig liver in lantana toxicity.