The anti-tumor action of Taxol was investigated in the changes of amino-acids involved in tumor cell survival. By tracing the intracellular amino-acid profiles of HeLa cells treated with non-conditioned and three conditioned media (Taxol, l-alanine, and Taxol + l-alanine), it was observed that an alteration of amino-acid metabolism participates in Taxol-induced death of HeLa cells. The contents of 18 out of 21 detected amino-acids are 5-95% and the ones of lysine and methionine are 158 and 117% of the corresponding contents in the control after treatment with Taxol for 24 h, respectively. Addition of l-alanine inhibited cell apoptosis upon Taxol treatment by partially blocking the increase of lysine and methionine and reversing decrease trend of alanine, glycine, and glutamic acid. These results suggest that interference of amino-acid metabolism might be an important mechanism of Taxol cytotoxicity.