Trehalose, and to some extent a few other carbohydrates, is capable of stabilizing the structure and function of isolated biological membranes during lyophilization. In this paper the results of investigations into the long-term stability of the lyophilized membrane-carbohydrate mixtures were reported. The effects of varying water content, oxygen level, and light on the rates of oxidation, browning, and degradation of biological activity were reported. The efficiency with which three carbohydrates stabilized membrane structure was also reported, with glucose shown to be less efficient than maltose or trehalose. Increased water content accelerated loss of biological activity, possibly because, under the same conditions, nonenzymatic browning and photooxidation were accelerated also. Glucose-containing samples were especially unstable at elevated humidities. Efficiency of preservation could be maximized by storage under conditions of low oxygen, low humidity, and dark, and by the inclusion of high levels of trehalose.