Direct ammonium fumarate production from glucose-based media with Rhizopus arrhizus NRRL 1526 was obtained using 2 kmol (NH4)2CO3 per m3 as neutralising agent and controlling mycelial growth by phosphorous (P) limitation. As the P level in the production medium was increased from 0 to 0.3 kg of KH2PO4 per m3, the fumarate yield decreased from 0.32 to 0.13 g per g of glucose consumed; maximum ammonium fumarate productivity (0.46 kg m-3 h-1) was obtained when using 0.1 kg phosphate m-3.