A total of 22 patients having hip replacements were studied to determine biochemically whether or not fat stitches cause fat necrosis. We found that fat necrosis, as measured by the triglyceride concentration of the drainage fluid, occurred in all wounds. The use of a fat stitch did not increase the amount of fat necrosis, but significantly reduced the amount of fluid drained (P less than 0.001; Student's t test). This retention of triglycerides is probably undesirable as they can act as a substrate for prostaglandin synthesis.