A variety of samples consisting of purified compounds (of various origins) and ethanol extracts from plants were assayed for their activity on the growth and initiation of crown-gall tumors on potato disks. The results demonstrated a high correlation between the ability of these compounds to inhibit the initiation and growth of crown-gall tumors on potato disks and their corresponding activity on the mouse P388 leukemia protocol. Of the 21 compounds tested to date, there were two false-positives and one false-negative.