The author has succeeded to induce heteroryon artificially on synthetic agar media in two vatrities of Aspergillus Awamori and two mutants of Penicillium chrysogenum Thom Q176 strain. The heterocaryon between the 5-9 and the N-19 varieties of Aspergillus Awamori was intermidiate between the two parental varieties so far as colour and form of the colony were concerned. The heterocaryon in Penicillium chrysogenum was induced between two ultra-violet ray mutans; the one, UY-3S strain former jagged colony producing a large amount of yellow substances: sorbicillin and penicillinic acid while the other, UW-1S strain formed round and colourless colony, though colour of spores of both strains were equelly white and quite indistinguishable. The conidia produced by the hetercaryon were green and contained yellow substances just as wild type Penicillium chrysogenum Thom Q 176 does. Variation of the characters in the heterocaryotic strains was continuous covering the whole range between two parents, the existence of colour substances and the jaggedness of colony, however, being closely associated. As the number of nuclei in cells of Penicillium usually reaches more than a dozen per cell, it may reasonably assumed that the variation of those chracters in the heterocaryon as stated above results from a combination of different number of nuclei from the two parental strains.