Dietary spice components have been screened for their protective effect against reactive oxygen species (ROS)-induced, lipid peroxide-mediated membrane and DNA damage and mutagenecity. A new, water soluble, 5-kDa peptide--Turmerin--from turmeric (Curcuma longa) has been found to be an efficient antioxidant/DNA-protectant/antimutagen. Turmerin forms 0.1% of the dry weight of turmeric and is obtained in a crystalline form. It is a heat stable, noncyclic peptide containing 40 amino acid residues, with a blocked N-terminal and leucine at the C-terminal. It is insensitive to trypsin and pepsin, heat, and uv radiation. Turmerin contains three residues of methionine which are partly responsible for the antioxidant activity. Turmerin at 183 nM offers 80% protection to membranes and DNA against oxidative injury. ROS-induced arachidonate release and the mutagenic activity of t-butyl hydroperoxide are substantially inhibited by Turmerin. Tumerin is noncytotoxic up to milligram concentrations, as tested by Ames assay and in human lymphocytes.