Narrowing effects of citrinin on representatives of major groups of the fungi were reported recently¹⁾. Besides the narrowing of growing hyphae, growth of short side branches in almost at right angles to the hyphal tips of Botrytis cinerea and also yeast-like growth of the the dimorphic fungus Paecilomyces viridis, can be induced by citrinin²⁾. The present report is con cerned with the effects of the antibiotic on permeability of Eremothecium ashbyi which is known to produce riboflavin.