Qualitative relationships between medium composition, Aspergillus niger morphology, and phytase production were investigated in submerged (SmF) and solid-state fermentations (SSF). Media composition and fungal morphology greatly affected phytase production in submerged culture. Addition of wheat bran, and consequently addition of a slow releasing organic phosphate source, enhanced A. niger growth and phytase production, in submerged and solid state culture. The fungal morphology in the presence of wheat bran changed from pelleted to filamentous in submerged culture. Filamentous mycelium and small pellets resulted in higher phytase activities than large pellets. Inoculation of solid-state fermentations with small pellets and free mycelial trees resulted in all cases in increased phytase activities. Large pellets were not suitable as a morphological form for SSF inoculum, unless they were homogenized. Homogenized large pellets led to SSF productivities similar to those from filamentous mycelia, irrespective of the medium type on which they were grown.