Baffling butadiene.

--The macrophage content of cell suspensions from naturally occurring mouse tumours has been assessed by the Fc-mediated phagocytosis assay, and the results compared with the individual tumour's capacity for spontaneous metastasis and with its pulmonary colonization potential after i.v. inoculation. It was found that these tumours differ in their properties from the transplantable fibrosarcomas studied previously by other investigators, in that the macrophage content of all the tumours was uniformly low, ranging from 2 to 9% (mean 4.2 + 1.80%) and there was no inverse correlation with frequency of spontaneous metastasis, which was low. When the tumours were inoculated i.v. there was also no correlation with colony-forming capability, which varied greatly between tumours. Lung secondary deposits contained 1-7-6% macrophages (mean 4-4 + 0.6%) with a lower phagocytic activity for antibody-coated red cells than in the primary tumour.