The histopathological effects of variable intraperitoneal doses of 5-fluorouracil (5-FU) on lung, testis and the urinary bladder of mice were studied. Following administration of 5-FU according to the dosing schedule used in this study various lesions appeared in the lungs and they included emphysema and thickening of the interalveolar septa due to congestion, hemorrhage and infiltration of mononuclear cells. In the testes and the urinary bladder, edema of the testicular interstitium,

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... on of the spermatocytes, lack of spermatozoa and hyperplasia of the transitional epithelium of the urinary bladder were seen. When the dose and time of exposure were increased additional lesions appeared and they included congestion of blood vessels within the testicular interstitium and hyperplasia of the interstitial cells. Congestion of blood vessels and fibrosis were seen within the submucosa of the urinary bladder, and in the lungs, peribronchiolar lymphoid hyperplasia was evident. From the results of this study it was concluded that 5-FU in the doses used in this study was associated with histopathological lesions in the lung, testis and urinary bladder of mice.