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This paper confirms results showing that TA3 tumour cells coated in vivo with immunoglobulins, lose some of the coat upon transfer to in vitro conditions. By labelling IgG isolated from the ascitic fluid of TA3 tumours it was found that the immunoglobulin coating TA3 cells is dynamically exchanged with immunoglobulin in the corresponding ascitic fluid. Some of the released immunoglobulin is in a degraded state as judged from the fact that most of the released material lost the antigenicity of intact immunoglobulin and has a lower capacity to precipitate with ammonium sulphate at 50% saturation. The degraded immunoglobulin has a higher binding efficiency to tumour cells. In vivo experiments demonstrated that the ascitic fluid of mice bearing TA3 and MCIM tumours contains a material which has some of the physicochemical properties of IgG but which does not precipitate with antisera directed aguinst IgG. [ABSTRACT FROM AUTHOR]