Spores of the fungus Humicola lutea 120-5 were entrapped with crosslinkable poly(vinyl alcohol) containing N-methylene acrylamide groups in the presence or absence of poly(ethylene glycol) of molecular weight 1000. Germinated mycelium from the entrapped spores was reused in 72 h batch culture for acid proteinase production. Maximal enzyme yield (25 000 U from immobilized mycelium in a flask) was reached in the third batch using crosslinked poly(vinyl alcohol) mixed with poly(ethylene glycol). In this case the apparent activity was 200% of the yield obtained by the immobilized system without poly(ethylene glycol) and was maintained over a period of 30 days. The half-life of enzyme biosynthesis was 14 batches (42 days) compared to 6 batches (18 days) for the biocatalyst without poly(ethylene glycol) and 4 batches (12 days) for the free cells.