This paper reviews methods which have evolved at the Research Triangle Institute during the last 15 years for the isolation and characterization of antitumor agents from plants. The isolation procedures stress mild, nonchemical methods. Solvent partition and the Craig Counter Current Distribution are used during the early stages of fractionation. Subsequent purification involves many types of chromatography: adsorption, partition, thin-layer, preparative thin layer, gel-exclusion, and medium- and high-pressure liquid chromatography. The pure compound is crystallized from a suitable solvent. The fractionation is monitored with in vitro and in vivo bioassays. Physical methods used for structure determination are: ultraviolet, infrared, and nuclear magnetic resonance spectrometry, and X-ray crystallography.