<p>5-fluorouracil is highly toxic drug with a narrow margin of safety. Therefore patients should be carefully supervised, since therapeutic response is unlikely to occur without some evidence of toxicity. Daily dose should not exceed 1 gram. Treatment should be discontinued promptly when one of the following signs of toxicity appears: Leucopenia (WBC under 3500/mm3). Thrombocytopenia (platelet under 100000/mm3). Stomatitis ( the first small ulceration at the inner margin of the lips is a signal for stopping treatment). Severe diarrhoea (frequent bowel movements and watery stools). Gastro-intestinal ulceration and bleeding.</p>