Aspergillus niger PM I was grown in a tubular loop and a stirred tank bioreactor. Batch fermentations were performed under various agitation conditions and pH. Citric acid, oxalic acid, extracellular polysaccharides and proteins were assayed. The following morphological parameters were measured : mean perimeter of clumps, mean perimeter of the central core of clumps, mean length of filaments and mean diameter:of filaments. Citric acid production and morphology in both reactors were dependent,on agitation intensity and pH. The length of the filaments was shown to be the only parameter that could be related to citric acid production in both reactors :the shorter the filaments the more citric acid was produced. However, for the same amount of citric acid produced the morphology of the organism grown in the stirred tank differed considerably from that grown in the loop reactor.