Abstract The concentration of the platelet-specific protein B-thromboglobulin (B-TG) was measured in early morning urine samples from 36 patients who had no evidence of renal dysfunction, after operation. Immediately following operation there was a steep rise in B-TG levels in urine, which returned to low levels in most patients during the first 3 postoperative days. Elevated levels of this protein after the third postoperative day occured in 87.5% of patients who had extensive deep vein thrombosis (DVT), whereas only 16.7% of patients who were thrombus-free had raised levels. Although not absolutely specific, urinary B-TG may be worthy of further investigation to determine its potential use as a screening test for DVT after operation.