In this paper, the connection between morphology, cephalosporin-C production and alternative respiration of Acremonium chrysogenum is examined. As demonstrated by chemostat experiments, the ratio of the filamentous and the yeast-like forms depended on the growth rate. The yeast-like form, but not the filamentous form exhibited cyanide-resistant alternative respiration. As a consequence, the yeast-like form was regarded to be more suitable for antibiotic overproduction.