The effect of different adenine-containing compounds on the NADP-/NAD-glutamate dehydrogenase (GDH) ratio was studied as a function ofyeast-mycelium transition in BenjaminieUla poitrasii. Under in vivo conditions, at a 5.0 mM concentration, cyclic AMP (cAMP) and dibutyryl cAMP maintained the cells in the yeast form for up to 7 and 5 h, respectively, and this was reflected in the patterns of GDH ratios observed. In vitro studies of phosphorylation and dephosphorylation have also been carried out, and the results suggest a possible correlation between cAMP, the GDH ratio, and cell form in B. poitrasii.The possible role of cyclic adenosine 3',5'-monophosphate (cAMP) in the differentiation of fungi has been studied by several researchers (11,14). The survey of data from other fungal species described above has already implicated the involvement of cAMP in Y--M transition as well as raised the possibility of a connection between cAMP and GDH activity levels (9,11,13