We used a human cDNA macroarray containing various oncogenes and tumour suppressor genes to assess gene expression profiles in early-passage Jurkat T lymphocytes treated with clinically relevant concentrations of the antitumour antibiotic daunorubicin. Several oncogenes and tumour suppressor genes were either up- or down-regulated depending on the daunorubicin concentration used. The expression levels of some of these genes were confirmed by semi-quantitative reverse transcriptase-PCR. We also compared the changes in cell-cycle distribution and the apoptotic morphological characteristics of the cells treated with daunorubicin, using flow cytometry and fluorescence microscopy. Exposure to 182 nM daunorubicin (its IC(75) in Jurkat T cells: where IC(75) is the drug concentration that inhibits growth by 75%) resulted in cell-cycle arrest in G(1) and almost immediate apoptosis. In contrast, decreasing the drug concentration to 91 nM (close to the IC(50)) caused G(2) arrest and cell senescence-like growth arrest, whereas features of apoptosis and necrosis appeared only after longer incubation times. Gene expression profiles, cell-cycle distribution, the presence of DNA damage and the time-dependent response of Jurkat T cells to cell death were correlated clearly. The general behaviour of the genes suggests that cell-cycle arrest and cell death follow distinct pathways depending on drug concentration.