Effect of beta-carotene on the inhibition of lung metastasis induced by B16F-10 melanoma cells was studied in C57BL/6 mice. Simultaneous administration of the compound after tumor induction produced a significant reduction (71.36%) in tumor nodule formation. Increased lung collagen hydroxyproline (22.37 microg/mg protein) in the metastasized lungs of control animals compared to the normal animals (0.95 microg/mg protein) was significantly reduced (4.19 microg/mg protein) in the beta-carotene treated animals. High amount of uronic acid (355.83 microg/100mg tissue ) in the metastasized control animals was significantly reduced (87.87 microg/100 mg tissue) in the animals treated with beta-carotene. Lung hexosamine content also was inhibited significantly in the beta-carotene treated animals (1.58 mg/100 mg lyophilized tissue) compared to the untreated control animals (4.2 mg/100 mg lyophilized tissue). The elevated levels of serum sialic acid and serum gamma glutamyl transpeptidase activity in the untreated control animals was significantly reduced in the animals treated with beta-carotene. Beta carotene treated animals were survived up to 69 days. Histopathology of the lung tissue also correlated with the above parameters and life span of the drug treated animals. Our results reveal the antimetastatic activity of beta-carotene which are abundantly present in green plants, vegetables and fruits.