Since soluble MUC1 SP, was neither detected in patient sera [34] nor in the concentrated supernatant of MUC1-positive tumour cell lines (unpublished observations), we suggest that: (a) As shown (figure 2A) these mechanisms are responsible for only a small fraction of the surface-bound MUC1 SP domain which cannot be detected by our assay, and/or, (b) the MUC1 SP released to the blood is immediately degraded by serum proteases. This evidence concerns the gene MUC1 and neoplasm.