Five amino acids are accumulated during vegetative growth of Neurospora crassa, particularly.during the prestationary growth phase. Alanine, glutamine, glutamate, arginine and ornithine.comprised over 80% of the total amino acid pool in the mycelium. Amino acid pools of different amino acid auxotrophs were followed during the partial transformation of a mycelial mat into an aerial mycelium. The mycelial mat under starvation and in direct contact with air rapidly formed aerial mycelium, which produced thereafter a burst of conidia. During this process,glutamine and alanine in the mycelial mat were consumed more rapidly than other amino acids;in the growing aerial mycelium, glutamate and glutamine were particularly accumulated. Of the amino acids that were initially accumulated in the mycelial mat, only a high glutamine pool was required for aerial mycelium growth induced by starvation. This requirement for glutamine could not be satisfied by a mixture of the amino compounds that are synthesized via glutamine amidotransferase reactions. It is proposed that glutamine serves as a nitrogen carrier from the mycelial mat to the growing aerial mycelium.