The production of equine influenza in Madin-Darby canine kidney (MDCK) cells in large-scale microcarrier culture is described with detailed on- and off-line analytical data during cell growth and virus replication. Metabolite concentration profiles for glucose, glutamine, lactate and ammonium are shown. Lactate and ammonium concentrations were always below inhibiting levels. Concentration profiles for essential and non-essential amino acids of the cell culture medium are discussed. During cell growth proline was released into the medium with a significant rate while two amino acids, serine and methionine were almost depleted. After infection, virus titer increased after a delay of 10-16 h whereas first changes in amino acid metabolism could be observed within 4h post-infection. Here, glutamate and aspartate increase correlated to virus release kinetics, indicating cell disruption and apoptosis. Starting with a moi of 0.025 resulted in a maximum virus yield of 2.4 log HA/100 microl at 44 h post-infection.