Consumption of edible oils contaminated with Argemone mexicana seed oil is known to cause various clinical manifestations. In the present study, the effect of dietary intake of argemone oil on histopathological changes, haematological indices and selected marker parameters of toxicity was investigated to observe the exact sites and mode of action of argemone oil in rats. Histopathological changes in the liver showed increased fibrosis, hyperplasia of bile ducts and congestion in a few portal tracts. Lungs of argemone oil-fed animals indicated congestion and thickening of interalveolar septa. Alveolar spaces were disorganised and irregular. Kidneys showed vascular and glomerular congestion and patchy tubular lesions. At 30 days only mild congestion was noted in the myocardium. Cardiac muscle fibres showed degenerative changes at 60 days which were more marked in the auricular wall. Haematological examination showed appearance of anaemia in experimental animals. Hepatic alkaline phosphatase, alanine transaminase and aspartate transaminase activities were inhibited by 30, 29 and 29% after 30 days of argemone intake along with concomitant enhancement in serum by 27, 29 and 66%, respectively. Liver showed decrease in glutathione (32-63%) content along with significant stimulation of lipid peroxidation (49-105%) in argemone-intoxicated animals. These results suggest that liver, lungs, heart and kidneys are the target tissues of argemone oil toxicity and that membrane destruction may be a possible mode of action.