Two commercially available bioreactor systems, CELLine and miniPERM, were evaluated for their ability to support the production of monoclonal antibody (mAb) from a variety of murine hybridoma cell lines. Production and purity of mAbs were compared between the two systems and with mouse ascites tumour fluid generation. The quality and purity of the mAb generated by each method was analysed on SDS-PAGE gels and the antibody immunoreactivity in each case was quantified by indirect ELISA tests. The relative benefits of conventional growth medium (Dulbecco's modified Eagle's media, DMEM) and serum-free medium (hybridoma serum-free media, H-SFM) using the miniPERM system were also analysed, in terms of the amount of antibody produced, cell concentration and specific antibody titre. In all cases, the CELLine units tested gave higher protein concentrations compared to the miniPERM system under the same conditions (means and 95% confidence limits are 4.2+/-0.8 and 2.1+/-0.8 mg/ml, respectively), yet the miniPERM system yielded greater total amounts over a similar culture period (428.7+/-243.3 mg compared to 183.3+/-100.9 mg in the CL-350 CELLine unit). When defined by specific ELISA titre, both bioreactor systems yielded mAb levels that compared favourably with those derived from ascites. In addition, SDS-PAGE analysis indicated that the bioreactor antibody product was relatively free of contaminating protein, whereas ascites tumour fluid preparations displayed significant levels of extraneous protein. This study has shown that both bioreactor systems are acceptable in vitro alternatives to the in vivo production of mAbs in mice.