In order to produce, economically, bioinsecticides of Bacillus thuringiensis, complex media based on gruel were used. Hydrolytic activities involved in the assimilation of the carbon and nitrogen substrates by a B. thuringiensis subsp. kurstaki strain, named BNS3, were investigated. The production of proteases and amylases fluctuated greatly when the bacterium was grown on crude or enzymatically prehydrolyzed gruel, indicating the importance of induction events in their syntheses and inferring the ability of the strain to grow and to produce efficiently delta-endotoxins on complex substrates. Proteases, produced on crude gruel, were separated by ammonium sulfate fractional precipitation. Four protease pools were harvested. Characterization of all the proteases showed that they exhibited different behaviours toward pH, temperature, and thermostability, indicating differences among them. BNS3 proteases were shown to be neutral metalloproteinases, and salt and sodium dodecyl sulfate (SDS)-tolerant. One protease fraction exhibited almost 100% activity at wide ranges of pH (7-10) and of temperatures (30-80 degrees C), which is very particular for known B. thuringiensis proteases.