The responses of a number of wood-rotting fungi to culture filtrates of Phellinus contiguus strain GWR, which contained a factor active in self-induction of precocious fruiting, were tested by means of a bioassay. Fruiting of a second isolate of P. contiguus was stimulated by active filtrate and the responses of single basidiospore progeny of GWR ranged from nothing to full fruiting. In similar bioassays culture filtrates from 13 out of 16 single spore progeny stimulated fruiting in GWR but production of active filtrate did not correlate with capacity to respond. Other wood-rotting fungi (two other strains of P. contiguus, P. occidentalis, P. ferruginosus, P. igniarius and P. pini, Phylloporia ribis and Trametes versicolor) produced filtrates capable of inducing fruiting in P. contiguus strain GWR. P. pomaceus, lacked inducing activity and the inactive filtrate of Coniophora puteana was also inhibitory to mycelial growth. It is concluded that production of the factor inducing fruiting in P. contiguus is not species specific.