Three UV mutants of the chestnut blight fungus Cryphonectria parasitica were selected which lack the ability to  produce laccase activity when grown on tannic acid medium (Bavendamm reaction). Genetic analysis showed that all mutations were recessive and two were allelic and one was non-allelic. No significant change in virulence,  conidiation, and pigmentation was observed in the mutants as compared with the wild type strain.