Despite its nearly universal applications, protamine, a mixture of four major peptides with different sequences, is associated with clinically significant side effects. Through a well-designed enzyme digestion method, various low molecular weight prolamine peptides were obtained. Among them, two low molecular weight prolamine peptides with the same or even more potent heparin neutralization abilities as native prolamine were identified through both in vitro and in vivo tests. In addition, in vivo experiments showed that compared to native prolamine, these two low molecular weight protamine peptides were less toxic and would be safer for clinical use. (c) 2005 Elsevier Inc. All rights reserved.