The puryose of this study was to decide the optimal screening method for the detection of antitumor substances, to suggest the stage of screening for unknown compounds as to antitumor agents. Using an established screening system of clonogenic and colorimetric assay(MTT assay, BCA asssy, and SRB assay), the sensitivity of known antitumor agents was measured against twenty-four t.umor cell lines. In the result of compared data gener- ated with each colorimetric assay and clonogenic essay, Good correlation for MTT versus clonogenic assay against eaeh antitumor agents(ADR, BLM, and MMC)was 40%, 50%, and 67%. In the result, optimal screening method for the detection of antitumos substances was MTT & clonogenic assay. In order to take optimazied screening system, two-stage strategy can be used. In the first stage, substances would be tested in the MTT assay. In the scecond stage, the first stage-positive substances would be tested in the clonogenic assay.