To measure the pre- and postoperative tear fluid tumour necrosis factor-alpha (TNF-alpha) concentration and release in patients undergoing excimer laser photorefractive keratectomy (PRK).Tear fluid samples from 18 PRK patients were collected with scaled microcapillary tubes preoperatively (day 0), on the second (day 2), and on the seventh (day 7) postoperative days. The TNF-alpha concentration was measured using a double antibody radioimmunoassay, and the TNF-alpha release was calculated by multiplying the concentration by the tear fluid flow in the collection capillary.The mean tear fluid flow in the capillary was 22.5 microliters/min (range 1.5-93.2) on day 0, 80.7 microliters/min (3.0-219, p = 0.0002) on day 2, and 14.6 microliters/min (1.8-41.7, NS) on day 7. The mean TNF-alpha concentration and release values were: day 0, 358 ng/I (110-680) and 9.5 pg/min (0.2-37.5, NS); day 2, 417 ng/l (< 5-750, NS) and 28.6 pg/min (0.6-81.5; p = 0.003); and day 7, 320 ng/I (< 5-735, NS) and 4.8 pg/min (0-25.4, NS), respectively.TNF-alpha appears to be a component of normal tear fluid. In spite of hypersecretion caused by the corneal wound, TNF-alpha concentrations remain constant during wound healing. TNF-alpha release increases significantly during the 2 postoperative days following PRK, suggesting a role in corneal wound healing.