Preparations from yeast have been used for a long time for cosmetic and pharmaceutical purposes. Studies have identified glucan from the cell wall of baker's yeast as an immunologically active agent. Glucan is a poly beta-( 1-3)-linked glucopyranose of high molecular weight and belongs to the class of compounds known as biological response modifiers. Glucan preparations are involved in the activation of the body's natural defence mechanisms and in the acceleration of the skin's wound healing processes. In the skin, Langerhans' cells and keratinocytes are the immunologically competent cells. Recent studies indicate that UV irradiation can deplete the number and viability of these cells (immunosuppression). The use of non-specific immune-stimulators, such as glucan, is a new approach for improving the function of stressed skin. We have developed a process to modify pure glucan from baker's yeast to carboxymethyl glucan (CM-glucan), a water soluble product suitable for topical formulations. The functional properties of this new compound have been investigated in vitro and in vivo. Cell culture experiments showed that CM-glucan protects skin cells against the depletion of antioxidant molecules upon UV-A irradiation and promotes the growth of keratinocytes. In placebo controlled studies with healthy volunteers, the pretreatment of skin with CM-glucan offered substantial protection against skin damage caused by a detergent challenge or UV-A irradiation. In addition, CM-glucan enhanced the renewal rate of the stratum corneum.