Autologous blood transfusion in surgery for cancer has been avoided because of the metastatic potential of reinfused malignant cells. This study determined whether viable tumour cells remain in the red cell concentrate after separation and whether blood transfusion filters remove these tumour cells before reinfusion. Units of banked blood were inoculated with tumour cell lines: breast cancer SKBr3; colon cancer COLO 320; lymphoma Daudi; erythroleukaemia K562. After processing with the Cell Saver, aliquots of the red cell concentrate and waste saline wash were examined for tumour cells and cultured. Tumour cells from all four cell lines were identified in the red cell concentrate but not in the waste saline wash. All the cell lines except Daudi grew from the red cell concentrate. Experiments on two of the cell lines (SKBr3 and COLO 320) were performed in which the red cell concentrate was either unfiltered (control) or filtered with SQ40S blood transfusion filter or RC100 leucocyte depletion filter. Both cell lines were present in the control samples and after filtration with SQ40S filters, and cells from these samples grew normally in culture. No tumour cells were evident after filtration with the RC100 filters and no growth of either cell line was found after 1 week in culture. The Cell Saver in combination with RC100 filters may be suitable for use during the surgical treatment of malignant disease.