Zymosan is prepared (Pillemer, L. and Ecker, E.E., (1941)) from actively growing yeast ( Saccharomyces cerevisiae ). After removal of cellular contents the isolated cell walls remain. This is zymosan and it is primarily composed of the highly cross-linked polysaccharides alpha-D-mannan, beta-D-glucan, and other minor polysaccharide polymers. Fresh zymosan, and especially zymosan stored as a dried powder, must be activated to develop its full complement-activating activity (Minta, J., 1983). This is done by refluxing zymosan in saline at 100 o C for two hours. This process has been performed for customers on the zymosan offered by CompTech and it is sold as a pre-activated suspension in saline. The product has been shown to be stable for four years if kept frozen. It is stable at 4 o C for several months if not contaminated by microbial growth.