Amino acids of transport systems A and N play certain important role in cell activation. For example, the presence of these amino acids is essential in the induction of ornithine decarboxylase by growth factors and hormones. At mM concentrations, each of these amino acids, particularly L-asparagine, can also induce the enzyme without being further metabolized or incorporated into proteins. We have reported that the addition of 10 mM L-asparagine to quiescent Reuber's H-35 rat hepatoma cells caused an immediate and transient increase in intracellular pH. Here we report that concomitant with the intracellular alkalinization was an increase in H+ extrusion which was amiloride-sensitive and Na+-dependent. The induction of ornithine decarboxylase by L-asparagine was also amiloride-sensitive.