Abstract: Short-term cultures of human leukemic cells were utilized to study the antitumour effect of eight drugs commonly used in clinical medicine. Cytotoxic effect was demonstrated with nitrogen mustard, nitromin, sarcolysin,HOBOэMσиXиH thio-TEPA and myleran at concentrations of 7, 10, 25, 35, 100, and 100μg/ml respectively. No effect on the leukemic cells was observed with 6 MP and aminopterin. With the same culture technic twenty four compounds of various structures were screened for antitumour activity. Among these nine were found to have an injurious action on the leukemic cells in vitro, and besides, they were shown in in vivo experiments to possess also an inhibitory action on the growth of several transplantable animal tumours. The remaining fifteen compounds exhibited no effect on the leukemic cells in the culture, nor did they affect the growth of transplanted tumours. The close parallelism between the results of the in vivo and in vitro experiments indicates that this tissue culture method could be used effectively for screening antitumour drugs.