Activation of blood coagulation is a common complication of cancer in man and experimental animals. The causes of such activation may be multifactorial, but increased production of tissue factor (TF) by the host mononuclear cells may be involved. TF is not only produced by human monocytes (mTF) and tumour cells, but is also found in urine (uTF), where measurements might be clinically important. Using a highly reproducible (intra-assay CV 2โข3 per cent and inter-assay CV 8โข1 per cent) one-stage kinetic chromogenic assay (KCA) developed by this group, uTF levels were measured in controls [healthy volunteers (n=57), patients with renal stones and a normal ESR (n=30)] and in patients with benign and malignant diseases of the breast (n=94) and large bowel (n=62). Each benign disease group was sub-divided into inflammatory and non-inflammatory categories. There were no significant differences between the controls and the benign non-inflammatory groups, so they were unified for further analysis. Malignant groups, irrespective of tumour types, showed significantly higher uTF levels than controls (p<0โข001 for breast and p<0โข01 for large bowel). Similarly, breast and colorectal benign inflammatory groups showed significant increases over controls (p<0โข01 and p<0โข001, respectively). Patients with malignant disease showed uTF activity above the upper quartile range of the normal control group for breast, 77โข3 per cent, and large bowel, 73 per cent. uTF levels were related to histological tumour grading and were higher in non-surviving patients. In conclusion, uTF levels are raised in malignant and inflammatory disease compared with controls and patients with non-inflammatory conditions. uTF levels may reflect tumour progression.