AbstractThis is a preliminary report that shows that supplemental potassium partially prevents 1,2‐dimethylhydrazine (DMH) induction of tumors of the small intestine in Sprague‐Dawley rats. Male rats were injected weekly with 20 mg DMH/kg body wt for 20 weeks. Potassium chloride was provided in the drinking water one week before the first DMH treatment and was continued until sacrifice 14 weeks after the last DMH treatment. There were four groups of rats and they were identified as follows: DMH, DMH + K, K, and untreated control. Based on 24‐hour food and water consumption data and food and water compositions, rats provided 0.5% potassium (from KCl in the drinking water) were ingesting 287.5±9.2 mg potassium per 24 hours (K/Na = 4.18) and the unsupplemented groups were ingesting 180.3±18.4 mg potassium per 24 hours (K/Na = 2.62). At sacrifice, the incidence of DMH‐induced small intestinal tumors was significantly (p<0.05) reduced from 46% (6/13) in the DMH group to 6% (1/17) in the DMH + K group (p<0.05). The potassium supplement also significantly (p0.05). Based on the complete blood count and other blood parameters measured, the level of potassium supplement used induced no apparent toxic effects. The liver glutathione S‐transferase activity was increased in potassium‐supplemented groups, suggesting that prevention of DMH carcinogenesis by potassium might at least be in part attributed to the enhancement of a detoxification pathway.