For quantitative analysis of wound healing in surgical patients, samples of wound fluid were collected through a silicone rubber tube and their concentration of the aminoterminal propeptide of type III procollagen was measured with a specific radioimmunoassay. Peritoneal fluid, collected through an abdominal drain, and serum were also analyzed. At day 1 after operation, the mean concentration of the propeptide was 30 times higher than the mean preoperative serum level (2.5 micrograms/L). A significant increase (p less than 0.001) occurred at day 3 in the wound and at day 2 in peritoneal fluid. At day 5 the mean wound concentration (2670 micrograms/L) was 1000 times higher than the serum level. In serum a small but significant increase (p less than 0.05) was found at days 5 and 30. The increase in wound fluid resulted from the intact, liberated propeptide, indicating that the results reflect the synthesis of type III collagen deposited in the wound. This procedure offers a quantitative tool for wound healing studies. Other extracellular matrix components can also be measured, the sequential pattern of their appearance can thus be assessed, and disturbances and treatment effects in wound healing can be detected.