Recent studies have demonstrated the apoptosis-inducing potential of epigallocatechin gallate (EGCG), a major component of green tea, against various cultured cell lines. By using an amino acid analyzer, we investigated here the possible changes in the amino acid pool and utilization during the apoptosis of HL-60 cells induced by EGCG or gallic acid, a structural unit of tannin. Sublethal concentrations of EGCG initially elevated and then reduced the intracellular concentrations of most of amino acids except for glutamic acid and aspartic acid, whereas lethal concentrations of EGCG continuously reduced these amino acid pools during 6 hours. Both sublethal and lethal concentrations of gallic acid initially elevated and then reduced these amino acid pools. Both inducers elevated the intracellular accumulation and production of arginine and extensively reduced the utilization of other amino acids. These data demonstrate that EGCG showed more severe effects on the amino acid pool and utilization than gallic acid, which may explain, at least in part, the difference in apoptosis-inducing potential between these inducers.