Timonacic is a cyclic sulfur amino acid derivative with potential antineoplastic and antioxidant activities. Timonacic may induce malignant cells to revert back to an untransformed state. It may also restore contact inhibition, a phenomenon characterized by the paracrine inhibition of mitosis following the formation of a critical cell mass, presumably the result of cell-to-cell signal transfer. Timonacic may also produce antioxidant effects secondary to its release of cysteine and restoration of glutathione concentrations.