Male Lobund strain Sprague--Dawley (SD) rats respond to single doses of methylazoxymethanol acetate (MAM) with high incidence of intestinal tumors within 5 months. Some non-steroidal anti-inflammatory drugs (NSAIDs) can block the synthesis of prostaglandins (PGs) and also interfere with tumor growth. A new class of NSAID, piroxicam, was added to the feed of MAM-treated rats. When examined 150 days later, there was a significant reduction of tumor-bearing rats and of tumors/rat compared to controls on drug-free feed; and there was no evidence of toxicity.