Aspergillus niger IMI 41873 was cultured by the method of synchronous and submerged culture. Its sporulation occurred in the culture. Ribonucleic acids were extracted at each stage of life cycle. These RNAs were digested, separated and determined by P.E.I. cellulose TLC and HPLC methods. The levels of ribonucleic acids in sporulating mycelia were higher than those of conidiophore and phialide forming mycelia. Inosine 5-monophosphate and adenosine 5-monophosphate derivatives were found in HPLC separations. The levels of inosine 5-monophosphate and adenosine 5-monophosphate derivatives per ribonucleic acid were constant through differentiation. After the standard purine necleosides and boiling water extracts from A. bisporus, F. velutipes and L. edodes were added into the culture, their effects on sporulation were examined. Sporulation was greatly enhanced in each adding experiment.