A linear relationship between total solid concentration (TSC), delta-endotoxin production [Cry = 0.2795(TSC)-0.2472, R-2 = 0.8644] and poly-beta-hydroxybutyrate (PHB) accumulation [PHB = 0.1327(TSC) + 0.3974, R-2 = 0.9877] in Bacillus thuringiensis var. kurstaki HD-73 was observed. A similar correlation between delta-endotoxin and PHB accumulation [Cry = 2.1573(PHB)-1.1248, R-2 = 0.9181] was found. A minimum PHB accumulation of 0.52 mg l(-1) was required before the onset of delta-endotoxin production.