In this study, various nutritional and cultural parameters influencing diptera-specific delta-endotoxin synthesis by Bacillus thuringiensis subsp. israelensis HD500 were investigated. Of various inorganic nitrogen sources, the highest yields of Cry11Aa and Cry4Ba proteins were obtained on (NH(4))(2)HPO(4). Among carbon sources, inulin, dextrin, maltose, lactose, sucrose, whey and glycerol were all stimulatory, while glucose, starch and molasses were suppressive. High concentrations of inorganic phosphate (50 to 100 mM K(2)HPO(4)) were required for an effective synthesis of Cry4Ba. Mn was the most critical element for the biosynthesis of both toxins at 10(-6) M concentration. Mg and Ca favored production when provided at 8 x 10(-3) M and 5.5 x 10(-4) M concentrations, respectively, while Fe, Zn and Cu negatively influenced biosynthesis. Cry4-toxin synthesis was best at neutral pH and also when the organism was grown at 25 degrees C. Throughout the study, the extent of growth and sporulation of the producer organism was also monitored.