The role of surface adsorption in the disappearance of secreted foreign proteins from the medium of transgenic plant cell and organ cultures was investigated. When mouse monoclonal IgG1 was added to sterile plant culture media in glass shake flasks, the antibody concentration declined rapidly demonstrating that antibody was labile in the plant culture environment even in the absence of biomass and proteases. Elution of bound antibody from the surfaces of the flasks indicated that adsorption had contributed to the observed loss of antibody from solution. Antibody retention in sterile plant culture media was improved significantly when protein-resistant polymer coatings were applied to the glass vessels containing the antibody solutions. Pluronic F127 applied at a concentration of 1 mg mL(-1) to a primary dimethyldichlorosilane layer on glass yielded the best results in sterile Murashige and Skoog medium. When this coating was used in shake flasks for culture of transgenic tobacco hairy roots, there was a significant improvement in the accumulation of secreted recombinant antibody in the medium consistent with a reduction in antibody adsorption. Medium antibody levels eventually declined, however, as medium protease concentrations rose rapidly towards the end of the culture period. This work demonstrates that surface adsorption reduces the medium antibody titre observed in transgenic plant tissue cultures.