Bulk commercial grain, such as soybeans and wheat, may be contaminated by nongrain impurities, including jimson weed seeds, that coexist with the crop to be harvested. The present study was undertaken to determine the content of the major alkaloids of jimson weed seeds, atropine and scopolamine, as well as protein, carbohydrate, fat, mineral, hemmagglutinin, and tannin. Combined GC-MS analysis of a jimson weed seed extract revealed the presence of atropine and scopolamine plus possibly three additional tropane-like alkaloids. An improved HPLC procedure showed that the alkaloid concentration in samples obtained from different parts of the United States varied by as much as 50%: 1.69-2.71 mg/g for atropine and 0.36-0.69 mg/g for scopolamine. The presence of a strongly fluorescent green compound of unknown structure is also described. Baking experiments with jimson weed seed fortified wheat flour showed that atropine and scopolamine largely survive bread-baking conditions. Jimson weed seeds do not contain protease or amylase inhibitors. These observations provide a rational basis for relating seed composition to biological effects in animals and for assessing the possible significance of low levels of the seeds in food-producing animals and in the human diet.