Although glucocorticoid is essential in the treatment of pediatric acute lymphoblastic leukemia (ALL), their precise mechanisms of action remain unclear. We used DNA microarray to evaluate prednisolone-regulated genes in pre-B-ALL cells from 2 pediatric patients. We found up-regulation of 26 genes in ALL cells from both patients, compared with peripheral normal B lymphocytes before maintenance chemotherapy. Treatment with prednisolone for 48 hours induced down-regulation of 5 genes (terminal deoxynucleotidyl transferase, heparin-binding epidermal growth factorlike growth factor, pre-B-lymphocyte genes 1 and 3, and immunoglobulin lambda-like polypeptide) among 26 specifically expressed genes in pre-B-ALL cells from both patients.