ABSTRACTThe lag phase encountered during the germination of basidiospores ofSchizophyllum communewas extended by 5–8 h upon the addition of cell-free extracts prepared from dikaryotic fruitbodies; after this delay, germination progressed normally. Bovine serum albumin did not have any inhibitory effects on germination. This delay of germination was dependent on the amount of protein in fruitbody extracts, with maximum effects being observed at 400μg protein/ml. Treatment of spores with fruitbody extracts for as short as 5 min was sufficient to cause maximal delay of spore germination. Addition of fruitbody extract to spores after eight hours of inoculation in broth had no effect on germination. This inhibitory activity present in fruitbody extracts was specific in that basidiospore germination was only inhibited by cell-firee extracts prepared from homologous dikaryotic fruitbodies. The delaying substance was sensitive to proteases and heat but unaffected by DNase or RNase, suggesting that the factor is a protein.