The involvement of the regulatory mechanism induction in the biosynthesis of polymethylgalacturonase (PMG) by immobilized cells of Aspergillus niger 26 was studied. The immobilization altered the spectrum of pectin-degrading enzymes. The free cell cultures produced four pectinolytic enzyme activities, namely PMC, polygalacturonase (PG), pectinesterase (PE) and pectinylase (PL),while the entrapped mycelium synthesized PMG and PG only. The best inducer for PMG synthesis was highly esterified apple pectin. The effects of various pectin concentrations and time of incubation with inducer showed the induction model of PMG biosynthesis. The deinduction experiments provided evidence that the presence of the inducer in every cycle was obligatory for the PMG biosynthesis during repeated replacement cultivation.