<jats:title>Abstract</jats:title><jats:p>The inhibitory effect of rotundifuran, a labdane type diterpene isolated from the fruit of <jats:italic>Vitex rotundifolia</jats:italic>, on the proliferation of human myeloid leukaemia HL‐60 cells was examined. The concentration required for 50% inhibition of the growth after 96 h was 22.5 µ<jats:sc>M</jats:sc>. The mode of cell death induced by rotundifuran was found to be apoptosis, which was judged by the morphological alteration of the cells and by the detection of DNA fragmentation using agarose gel electrophoresis. The degree of apoptosis was quantified by a sandwich enzyme immunoassay and flowcytometric analysis. These results suggest that rotundifuran may be used as a potential chemopreventive and chemotherapeutic agent. Copyright © 2001 John Wiley & Sons, Ltd.