Fruiting genes in Schizophyllum commune are controlled by the mating-type genes and other regulatory genes. To examine whether differential accumulation of mRNAs for these fruiting genes is caused by transcriptional regulation, run-on transcription assaYs were performed with nuclei isolated from cultures differing in expression of these genes. It could be shown that accumulation of mRNAs followed enhanced transcription of most of the fruiting genes. Transcription continued during subsequent decrease of these mRNAs. In young not-yet-fruiting dikaryons and non-fruiting monokaryons the fruiting genes appeared to be transcribed at a low basal level. The GPD gene was used a control in these experiments and was transcribed at all stages