The study of the high reversion frequency of the nic-2 mutant of Coprinus radiatus has been carried out with the help of homothallic strains and by selecting for diploids. Homothallic strains revert at meiosis with the usual frequency of about 20%; this is definitely in favor of the high reversion frequency being an intrinsic property of the mutation. Diploid nic-2 strains also exhibit the usual reversion frequency at meiosis but no more than haploid strains or dicaryotes do, they do not revert during vegetative growth. The reversion is therefore not directly correlated with the diploid state. The possible nature of the nic-2 mutation and how its reversion could occur are discussed.