OBJECTIVE: Garden cress (Lepidium sativum L.) is an important herb in traditional medicine used to improve production of breast milk in women and semen in men. In the present research the authors evaluated its ability to destroy leukemic cancer (Jurkat E6-1) cells, using the alkaloid extract of this plant. METHODS: Constituents of the alkaloid extract were analyzed by gas chromatography-mass spectrometry (GC-MS) and their cytotoxicity in leukemic cancer cells and healthy peripheral blood mononuclear cells (PBMCs) was assessed. Cell death via apoptosis was confirmed by DNA laddering, caspase-3 activity, annexin V-fluorescein isothiocyanate and mitochondrial toxicity assays. The specific course of gene activation in treated cells was determined through quantitative polymerase chain reaction (qPCR). RESULTS: GC-MS analysis identified six alkaloids and proto-alkaloids, namely, benzyl isothiocyanate (1), 2-ethoxy-4H-3,1-benzoxazin-4-one (2), (4R)-2-(2-aminophenyl)-4-phenyloxazoline (3), 5-acetyl-1,2-dihydro-6-methyl-2-oxo-4-phenyl-3-pyridinecarbonitrile (4), benzo[b][1,8]-naphthyridin-5(10H)-one,2,4,7-trimethyl (5) and 1,4-diaminoanthraquinone (6), in the alkaloid extract of L. sativum. Of these, compound 1 was previously identified in the seeds of L. sativum. Exposure to the alkaloid extract caused death of Jurkat E6-1 cells, with median lethal concentration (LC) of 75.25 µg/mL. However, the alkaloid extract also showed a nontoxic and proliferative (1.6-fold) effect in healthy PBMCs. Further experiments performed with Jurkat cells at LC and sub-LC doses demonstrated DNA fragmentation, activation of caspase-3 and time-dependant phosphatidylserine translocation (apoptosis) from inner to outer cell membranes. Cell toxicity and assessment of adenosine triphosphate level, together with using qPCR to evaluate expression profile of major apoptosis genes, revealed that apoptosis may be induced by disruption in the mitochondrial outer membrane potential, through activation of extrinsic and intrinsic apoptosis pathways in Jurkat cells. CONCLUSION The ability of the alkaloid extract of L. sativum seeds to induce apoptosis indicates a potential pharmacological use in cancer chemotherapy. The separation of individual active compounds and further in-depth exploration of the molecular mechanism of apoptosis may lead to novel chemotherapeutic compounds in our future antineoplastic research.