Interspecific fusion products were obtained by protoplast fusion induced by polyethylene glycol, from auxotrophic mutants, Pleurotus cornucopiae and P. florida. The fusants were classified into allodiploidy, stable heterokaryon, and spontaneously segregated heterokaryons. Fruiting body of the clamped or clampless fusants was produced by light-dark cycle on the sawdust medium in glass bottles. Most of these clampless fusants produced mature basidiocarps. The pilei showed various mixed colors resembling the parents. All fruit bodies presented clamp connections except two fusants. When small tissues of stipe from basidiocarps were cultured on a complete medium, mycelial colonies grew more vigorously than that of the original clampless fusants. Five fusants in three crosses were analysed with the distribution of progenies and segregation of genetic characters by random spore analyses. The genetic markers were shown to segregate and recombine in the first generation of monospores isolated from basidiocarps. The analysis indicated the heter-okar-yosis and strong evidence for haploidy of vegetative nuclei, a sexual cycle consisting of nuclear fusion and meiosis. Genotypes of a large number of auxotiophic progenies were not detected. The aberration ratio of segregants indicated the gene interaction resulting from different genome structure between vegetatively incompatible species.