Monoclonal IgA antibodies have been produced by a hybridoma cell line grown in different bioreactors using serum-containing and protein-free media in both basal and fortified versions. The effects of culture conditions on IgA production and quality have been studied using an anti alpha-chain ELISA, an antigen-specific ELISA, and anti alpha-chain Western blotting from which the fractions of the various IgA molecular forms were estimated by densitometry measurements. In stirred-tank reactor (STR) batch cultures, a significant increase in final IgA concentration (220-720%) was obtained in both media types due to amino acid supplementation; in protein-free media, the productivity of total IgA was slightly lower, but the fraction of antigen-binding IgA was larger (81% versus 60%). In hollow-fiber reactors, the IgA concentration was strongly dependent on the harvesting frequency, and thus varied over a wide range (0.5-14 g l(-1)). Compared with IgA produced in STR cultures, larger fractions of polymers and aggregates were observed. The fraction of antigen-binding IgA dropped below 40% in both media types when the total IgA concentration exceeded 1-3 g l(-1). Further characterization of the various molecular forms will enable the determination of the optimum culture conditions for the production of the complete molecule (sIgA).