A steady state kinetic study was carried out with the glutamate dehydrogenase from the thermophilic, archaebacterial isolate AN1. Initial velocity studies of the oxidative deamination reaction showed the mechanism is sequential and indicated that the order of substrate addition is random, while inhibition studies with products and substrate analogues suggested a strong preference for NADP⁺ to bind first. Initial velocity studies of the reductive amination reaction showed that the mechanism is sequential and indicated that the order of substrate addition is random, while product inhibition studies and the effect of substrate saturation on the initial velocity suggested that the preferred order of substrate addition is NADPH, 2-ketoglutarate, ammonia.