Wound healing was studied in 95 jaundiced patients and 123 anicteric patients using skin prolylhydroxylase activity as an index of collagen synthesis. The mean (s.d.) value of skin prolylhydroxylase activity in jaundiced patients was significantly lower than that of controls in the preoperative period (40.1(19.2) versus 369.2(32.2) c.p.m./mg protein, respectively, P less than 0.001). Before operation there was a significant difference between patients with benign or malignant obstruction of the biliary tree (55.0(12.3) versus 25.2(10.4) c.p.m./mg protein, respectively, P less than 0.05). In patients with benign obstruction skin prolylhydroxylase activity returned to normal values (326.3(53.1) c.p.m./mg protein, P less than 0.001 versus preoperative values), while in patients with malignant lesions skin prolylhydroxylase activity increased significantly with respect to the preoperative period (25.2(10.4) versus 82.9(14.3) c.p.m./mg protein, P less than 0.01) but was still below normal values. Abdominal wound dehiscence was more common in jaundiced patients (six of 95) than in the anicteric group (two of 123). This complication appeared to be associated with a low skin prolylhydroxylase activity.