Tuftsin, discovered as a physiological phagocytosis-stimulating factor for neutrophils, has also been shown to have antitumor activity in our L1210 leukemia and Cloudman S-91 melanoma systems. In view of this, we propose to carry out the following objectives: 1. To produce a large quantity of pure tuftsin by employing chemical syntheses and chromatographic procedures. 2. To examine antineoplastic activity of pure tuftsin in vivo and in vitro. 3. To adapt the radioimmunoassay for tuftsin and determine the serum levels of tuftsin among normal and various populations of patients with tumors. 4. to perform the minimum toxicity study of the synthetic tuftsin to prepare for the possible future clinical use of tuftsin. Since we have modified the emphasis of this grant proposal during its revision, we believe it could best be reviewed by a study section other than Experimental Therapeutics. We would like to suggest the following: Immunological Sciences Study Section (1st preference) or Pathology B Study Section (2nd preference).