Human alpha (1)-antitrypsin (AAT) was produced in the recombinant yeast Saccharomyces cerevisiae ATCC 20699 grown in batch and fed-batch culture. The final biomass concentration and antitrypsin concentration attained were similar to 55 g .L-1 and 1.23 g .L-1, respectively, in the fed-batch. The maximum productivities of biomass and antitrypsin were 1.6 and > 0.04 g L(-1)h(-1), respectively, or substantially greater than the highest productivity values reported in the past. For recovering the antitrypsin, the cell slurry was concentrated 4-fold (231 g .L-1 biomass, 122 min of processing) by cross-flow microfiltration and the cells were disrupted by bead milling (3 passes of 3 min total retention time). The cell homogenate was treated with aluminum chloride or PBS (pH 7) to aid separation of the cell debris by flocculation and sedimentation. The clarified cell homogenate was subjected to ammonium sulfate fractionation to precipitate the recombinant antitrypsin. The AAT precipitated at 45-75% saturation of ammonium sulfate, depending on the age of the homogenate. The crude AAT in the homogenate degraded at room temperature (25 degreesC), with a zero order deactivation rate of 1.815 x 10(-3) +/- 3.43 x 10(-4) g AAT L(-1)h(-1).