Reports from Australia of illness in consumers eating bitter squash prompted a 10-wk mouse-feeding study containing increased levels of the fruit of two cultivars of Cucurbita pepo , L., 'Blackjack' and 'Straightneck', and an accession of the bitter species, Cucurbita texana , Gray, was conducted. The latter produced poor growth, severe diarrhea, anemia and 40% mortality in mice fed diets containing 1% freeze-dried fruit. Diets containing 10 or 20% C. texana caused 100% mortality within a few days. The cultivar contained 3.56 and 1.39 mg per g of fresh fruit cucurbitacins E glycoside and I, respectively. The cultivars of C. pepo , 'Blackjack' and 'Straightneck', contained no detectable cucurbitacins; animals fed up to 20% freeze-dried squash in their diets showed no toxicity, with normal growth and hematology.