The production of extracellular inhibitors of papain and trypsin by Streptomyces sp. 22 was studied under different cultural conditions including complex and defined media, temperatures ranging from 18 degrees C to 37 degrees C and a variety of sole carbon and nitrogen sources. In complex nutritionally rich medium, maximal specific growth rates were obtained at 37 degrees C, whereas the highest specific production rates for both papain and trypsin inhibitors were registered at 18 degrees C. Studies on the effect of different carbon and nitrogen sources in defined media underline the importance of the nitrogen source as a strong regulator of the biosynthesis of both inhibitors. Enhanced formation of the inhibitory compounds occurred in the presence of casein. The dynamics of the formation of both inhibitors in defined media showed close association with growth. However, a partial separation of production phases for papain and trypsin inhibitors was observed in complex medium. The results imply differences in the regulation of biosynthesis of the two inhibitors.