Coprinus congregatus did not show any growth on a minimal medium in the presence of phosphinothricin which inhibited glutamine synthetase. Genetic transformation to phosphinothricin resistance in C. congregatus was carried out successfully by restriction enzyme-mediated integration. The procedure was improved to yield 550 transformants per Wg of DNA, and three laccase mutants were generated. The vector pBARGEM 7-1 which had the phosphinothricin resistance gene was detected in the restriction enzyme fragments of chromosomal DNA from the transformants by Southern hybridization. Transformants showed identical electrophoretic banding patterns but CL1430b had a faster moving band when analyzed by native PAGE. z