Investigation has been conducted to delineate the action of some phenolic compounds of natural origin in fourhuman tumor cell lines: acute myeloblastic leukemia (HL-60), chronic myelogenic leukemia (K-562), breastadenocarcinoma (MCF-7) and cervical epithelial carcinoma (HeLa). In cells grown in appropriate media the phenolicscurcumin, yakuchinone B, resveratrol and capsaicin exhibited growth inhibition as assessed by trypan blue dyeexclusion. It was evident from the results of the MTT reduction assay and [3H]thymidine incorporation into nuclearDNA that the phenolics were cytotoxic and inhibited cell proliferation. Dose response studies indicated curcumin tobe most cytotoxic towards HL-60, K-562 and MCF-7 but did not show much activity in HeLa cells. On the otherhand, yakuchinone B, although less active than curcumin, displayed cytotoxicity towards all four cell lines. Resveratrolwas cytotoxic only in leukemic cells, while capsaicin was marginally cytotoxic. All these phenolics did not elicit anycytotoxic activity as judged by the above parameters towards lymphocytes purified from normal human blood.When cells treated with phenolics were stained with propidium iodide and examined under a fluorescent microscope,characteristic apoptotic features such as chromatin condensation and nuclear fragmentation were observed. Scoringof cells with apoptotic and non-apoptotic features showed positive correlation of apoptotic index with dose of phenolic,and fragmented DNA extracted free of genomic DNA displayed on gel electrophoresis a typical ladder pattern.These phenolics which have human exposure are known cancer chemopreventive agents and their action as inducersof apoptosis in tumor cells suggest their potential use in a strategy for cancer control.