In the yeast, Candida nitratophila Shifrine et Phaff, the intracellular concentrations of α-amino acids decreased rapidly during N-deprivation, with the ratio of glutamine: glutamate (Gln: Glu) falling from 07 in NH4+-grown cells, or 0.5 in NO3−-grown cells, to 0.1 after 1 h. Addition of NH4+ to N-deprived cultures resulted in rapid increases in glutamate, glutamine and alanine with Gln: Glu exceeding 1.5 within 30 min. Recovery of other amino acids, such as arginine, was much slower. Addition of NO3, resulted in a less rapid increase in the concentration of some intracellular amino acids, including glutamate and glutamine, while levels of arginine continued to fall for 30 min after addition of this N-source. Gln: Glu was slow to rise in NO3− pulsed cells. Addition of NH4+ to cells growing on NO3− produced little change over the following 2 h other than decreases in arginine and histidine. Carbon deprivation resulted in a rapid decrease in levels of glutamate, glutamine and alanine, but not of aspartate (which this yeast is unable to use as a sole C-source for growth) or arginine. Gln: Glu increased during C-deprivation but fell within 10 min to normal levels on addition of glucose. It is concluded that, in C. nitratophila, Gln:Glu values correlate well with C-N status.