In this study, lesions of chronic toxicity induced by 2,4-dichlorophenoxyacetic acid (2,4-D) in male Sprague-Dawley rats was investigated. 2,4-D (30 mg/kg b.wt. in 0.5 ml saline daily) was given orally to male rats for six months. Histopathological examinations of tissue specimens revealed that liver, kidneys, lungs, heart, testicles, epididymis and brain were seriously affected after 2,4-D exposure. Liver showed vascular and hepatocellular changes. The hepatocellular changes were varied from necrobiotic changes to preneoplastic changes. Lesions in the kidneys consisted of glomerular swelling, glomerulonephritis and hyperplasia of the renal tubular epithelium. Lungs showed necrosis and sloughing of bronchiolar epithelial lining and heavy infiltration with lymphocytes. The heart exhibited hemorrhage and degeneration in the cardiac muscle. Necrotic orchitis and epididymitis were demonstrated. Hyperemia, edema, neuronal degeneration of ischemic type was observed in the brain. In conclusion, 2,4-D induced deleterious pathological effects on vital organs including preneoplastic changes in the liver.