Somatic compatibility is used to identify clones or vegetative compatibility groups (VCG) in fungal populations. For basidiomycetes, VCGs have normally been associated with either homothallic, non-outcrossing fungi or root decay fungi spreading by vegetative growth. A special instance is provided by the symbiotic relationships between woodwasps and the fungi Amylostereum areolatum and A. chailletii. This association results in clonal propagation, as the wasps (Sirex sp. and Urocerus sp.) transfer arthrospores of A. areolatum or A. chailletii during ovipositing in conifers. Identical isolates of the symbiont are normally carried by all the female offspring of one wasp. The presence of clones of A. areolatum and A. chailletii was tested through somatic compatibility shown in pairings of heterokaryons obtained from wasps, basidiocarps and wood. Isolates found more than 100 km apart within Denmark belonged to the same vegetative compatibility groups. In addition, A. areolatum isolates from Sweden and Lithuania were compatible with a Danish clone, in spite of the barrier of the Baltic Sea. The association between woodwasps and fungi thus creates dispersive clones or VCGs which are stable across time and space. The dispersal through basidiospores may be considered of less importance for A. areolatum, but common in A. chailletii.