The cytotoxic effect of the sesquiterpene lactone, parthenin was studied IN VITRO using cultured bovine kidney cells. The drug inhibited macromolecular synthesis. Fifty percent inhibitions in RNA, DNA and protein synthesis were observed when the cells were treated with parthenin at a final concentration of 1 \mu g/ml. The cytotoxic effect of parthenin was also evident by its ability to markedly inhibit the activities of key cellular enzymes after treatment of the cells with the toxin for 24 h