Intraocular pressure (IOP) control was studied retrospectively in two groups of 14 consecutive patients following trabeculectomy with adjunctive postoperative 5-fluorouracil (5-FU) treatment. In one of the groups (the early-treatment group), 5-FU injections were started 2.4 +/- 0.6 days postoperatively; in the other group (the delayed-treatment group), they were started only when clinical signs suggested impending bleb failure (12.6 +/- 5.4 days postsurgery). The patients in the two groups were age-matched and had a similar history of previous failed glaucoma operations or diabetes, both of which are considered indications for postoperative 5-FU injections. The mean number of 5-FU injections and the total dose in the two groups did not differ significantly (5.3 +/- 0.8 and 5.5 +/- 1.1 injections, respectively; 26.4 +/- 3.9 and 27.5 +/- 5.3 mg 5-FU total dose, respectively). The average follow up for the two groups was 16.7 +/- 2.5 and 16.9 +/- 2.7 months, respectively. With an IOP of 18 mm Hg or less with or without medications considered a success, 42.8% of the delayed-treatment and 71.4% of the early-treatment cases were successful. More medications were required in the early-treatment group. Postoperative transient corneal epithelial defects occurred in 71.4% and 78.4% of the eyes in the late- and early-treatment groups, respectively, an insignificant difference. Conjunctival wound leak occurred in one patient (in the delayed-treatment group).(ABSTRACT TRUNCATED AT 250 WORDS)