Cell aggregates of Cladonia miniata var. parvipes immobilized in calcium alginate were used to assay their ability to produce barbatic acid. Immobilisates were supplied with sodium acetate or calcium acetate as a precursor for phenol biosynthesis, with ampicillin to prevent bacterial conta mination. Barbatic acid was actively produced during incubation, although cell vitality progressively decreased. Calcium acetate increased the rigidity and mechanical resistance of immobilisates and produced cell plasmolysis. Ampicillin slightly improved the production of barbatic acid, probably by impeding the competition ofbacterial populations using acetate as a source for growth. Cladonia miniata var parvipes, alginate, ampicillin. barbatic acid, cell immobilization.