Using cultured cells derived from human malignant effusions, hetero-antisera were raised in rabbits. The antisera were sequentially absorbed on various human non-tumour cells, reactivity being monitored by immunofluorescence and 125I-labelled staphylococcal protein A assays. The absorbed antisera possessed common reactivity to all tumour cells assayed. This reactivity was not histogenically determined, and our data suggest that it was not directed to oncofoetal antigens
