In the 1970s chemotherapy has been successfully incorporated into curative primary treatment programs for various adult malignancies so that it is no longer solely palliative treatment for advanced disease. For at least three malignancies and tentatively a fourth (breast and colon carcinoma, osteosarcoma, and melanoma), certain groups of patients have had longer disease-free survival produced by the use of chemotherapy after surgical removal of the primary lesion. The potential impact on cancer mortality from these treatment results is obvious. We review here the fundamental laboratory concepts that have led to human trial of multimodal primary therapy regimens. Data from numerous clinical trials are analyzed, with delineation of the problems encountered in the interpretation of their results.