Aims: The present work aimed at evaluating the usefulness of selecting different kinds of biochemical mutants of Aspergillus niger to increase inulinase production in submerged culture. Methods and Results: Conidia of A. niger 13/36, an active producer of inulinase, were subjected to mutagenesis with both u.v. and N-methyl-N'-nitro-N-nitrosoguanidine (NTG), and the products were analysed for inulinase activity with our own diffusion plate method. As a result of mutagenization and selection for obtaining biochemical mutants ( e. g. surviving conditions of certain abiotic stresses, good growing on basal medium at 15 and 40 degreesC), A. niger strains resistant to these agents were obtained. Studies of the relationship between a criterion of selection and the frequency of mutation showed that the highest frequency of positive mutations in the second selection (86%) was obtained in mutants characteristic of the best growth at the low temperature ( 15 degreesC), when compared with the parent culture (28%). The most active mutants grown under stress conditions showed significantly higher inulinase activity (about 1.2 -4.5-fold), when compared with the parent strain. Conclusions: The studies presented seem to confirm a high effectiveness of selection in some kinds of biochemical mutants of A. niger with regard to increased inulinase activity. Significance and Impact of the Study: This screening strategy of mutants can be a contribution to modern commercial enzyme production.