Transgenic rice suspension cultures were utilized to produce a human therapeutic protein, recombinant (xi-antitrypsin (rAAT), in a cyclical, semicontinuous operation. Recombinant protein production was induced by removing the carbon source from the cell culture medium. The transgenic rice cells secreted the rAAT into the medium, and therefore medium exchanges could be performed for consecutive growth and protein expression phases. The process consisted of three cycles over a 25-28 day period, with growth phases lasting 4-6 days each and protein expression phases lasting 2.5-5 days each. Biomass and sugar concentrations, oxygen uptake rate, cell viability, culture pH, total extracellular protein, and active rAAT were measured throughout the cyclical process. The data profiles were reproducible between separate cyclical runs where, following each induction period, cell growth and viability could be reestablished once sucrose was added back to the culture. Volumetric productivities ranged from 3 to 12 mg active rAAT/(L day) for individual cycles with overall volumetric productivities of 4.5 and 7.7 mg active rAAT/(L day).