Stabilizing effect of several commonly used cryoprotectants, namely lactose, sucrose, and polyvinyl-pyrrolidone (PVP), on recombinant alpha 1-antitrypsin (rAAT) were studied. A solution of rAAT in a phosphate/citrate buffer (pH 7.0) was made with and without a given cryoprotectant and filled into small vials. The vials were frozen on shelf, at -40 degrees C in a lyophilizer. At the end of the freezing cycle, half of the batch was thawed at ambient temperature and the other half was continued to the completion of lyophilization. Sample vials taken before freezing, after thawing, and after lyophilization were analyzed for total rAAT protein, monomeric content, and elastase-inhibitory activity. Results indicated that neither freeze-and-thaw nor lyophilization caused any damage to rAAT, contrary to what was generally believed. The control formulation (i.e., without a cryoprotectant) performed as good as those containing cryoprotectants. Freezing rates and protein concentration in formulation did not influence the stability of rAAT either. Lyophilized rAAT samples retained the activity and purity during the 12 month stability period, at room temperature and 2-8 degrees C.