Six inositol-less mutants of N. crassa were grown for 5 days on minimal medium containing [U-14C]-D-glucose and myo-inositol (1-5I-'gjml). It was shown by a combination of electrophoresis, paper chromatography, and gas-liquid chromatography that in all cases a derivative of [14C]-myo-inositol which behaves as an inositol monophosphate ester was present in the mycelium.