Restriction enzyme anal. was used to evaluate genomic DNA methylation patterns in two different life cycle stages of the button mushroom Agaricus bisporus.The authors' investigation reveals that some degree of 5-methylcytosine occurs in this fungus.Furthermore, methylation may be partially or fully specific for the internal cytosine of the CCGG recognition sequence.Evidence for 6-methyladenosine, 5-hydroxymethylcytosine, and 4-methylcytosine was not found.Methylation of cytosine at C-X-G sequences, common in higher plants, was not detected in A. bisporus genomic DNA.Cleavage of sporophore and mycelial DNA by a wide range of Type II endonucleases gave no evidence of developmental differences in methylation.