The mating system of Pleurotus flabellatus was investigated using twenty monokaryons obtained from a single sporophore. All matings between pairs of monokaryons fell into four genotypic classes indicating that the fungus has bifactorial incompatibility. Considerable variation in growth rate was observed among monokaryons, the derived dikaryons and their component monokaryons. No correlation was found between growth rates of derived dikaryons and expected combined mean growth rates of their component monokaryons or the individual growth rates of monokaryons. The ability to produce fruit-body primordia in vitro on straw was not solely restricted to the dikaryons. Cultivation trials of derived dikaryons to select better strains over the parental dikaryon were promising.