Germlings of Phycomyces blakesleeanus were converted to protoplasts using an enzyme solution of chitinase and chitosanase. The protoplasts were regenerated to normal growing mycelia. Protoplasts of different auxotrophic strains fused in diluted natural seawater and in Ca(NO3)2 solutions. 36 prototrophic strains were isolated (Table 1). Their heterokaryotic nature was proved by the segregation of the markers in vegetative spores.