Humicola lutea 120-5 spores were immobilized in a mixed photo-crosslinked polyvinyl alcohol and calcium-alginate gel. Maximum enzyme synthesis was established with 1:8 (v:v) gel beads: growth medium inoculum and 48 h duration of one cycle. The free cells were very unstable in replacement fermentations. The operational stability of the immobilized system indicated the possibility of the application of Humicola lutea 120-5 in a semi-continuous process for the production of acid proteinase.