Isolates of the dry rot fungus, Serpula lacrymans , and of the morphologically similar wild merulius, S. himantioides , were investigated by amplified ribosomal DNA restriction analysis (ARDRA) of the internal transcribed spacer (ITS) region to prove this method as diagnosis tool for the economically important indoor rot fungi. The technique uses the polymerase chain reaction (PCR) to amplify the relatively variable sequences of the ITS region arranged between the highly conserved portions of the 18S and 28S RNA genes of the nuclear ribosomal DNA (rDNA) repeat unit. Subsequent digestion of the amplicon with restriction endonucleases may exhibit differences at species and subspecies level. Using the universal ITS 1/ITS 4 primer combination, the ITS region of all isolates of S. lacrymans and S. himantioides was amplified. The size of the amplified products was about 630bp in both species, as estimated from agarose gel electrophoresis. Digestion of the amplicon with the endonuclease pairs Alu I/ Hha I and Ava II/ Mbo II, respectively, revealed identical rDNA-ITS fragments for the isolates of both species, indicating their genetic relationship. On the other hand, digestion with Bgl I/ Hinf I and Hae III/ Taq I, respectively, separated the fungi by means of different fragment patterns. Thus, ARDRA-ITS proved to be suited for the identification of both fungi.