Since homocysteine metabolism is important in the control of normal and abnormal growth, three homocysteine derivatives were synthesized and tested for effects on the growth of transplanted murine adenocarcinoma. Arachidonoyl homocysteine thiolactone (HCT) amide decreased growth, and oleoyl HCT amide increased growth of the neoplasm. Pyridoxal HCT enamine decreased the growth of the neoplasm when given for 2 weeks prior to transplantation, but the compound had no effect when given after transplantation. The two inhibitory substances were tolerated well by normal mice except in high doses. These findings suggest an approach to prevention and therapy of human malignancy which utilizes homocysteine derivatives of normal biochemical constituents.