Purpose: To evaluate the conjunctival structure and inflammatory cell counts and to determine the predictive value of these histological parameters for postoperative intraocular pressure (IOP) levels after trabeculectomy. Methods: A clinical and histological study was performed on consecutive patients. Postoperative (mean 32.8 +/- 18.4 months; range 6-60 months) conjunctival biopsies of 36 eyes of 28 primary open-angle glaucoma patients who had trabeculectomy between 1992 and 1995 were included in the study. According to postoperative pressure control, patients with less than or equal to 16 mm Hg and those with > 16 mm Hg were taken as groups 1 and 2, respectively. The control group (group 3) consisted of 15 age-matched patients without glaucoma, who had received no topical therapy. We compared the conjunctival structure and cell counts within these groups. Goblet cells, acute inflammatory cells, chronic inflammatory cells, fibroblasts, epithelial thickness, vascular density, mucopolysaccharides and collagen compositions were determined in groups 1, 2 and 3. Results: The number of goblet cells was significantly higher in group 1 (6.74 +/- 7.23) than group 2 (3.09 +/- 2.77; p = 0.017). No statistical difference was observed in the number of acute inflammatory cells, chronic inflammatory cells, fibroblasts, epithelial thickness, vascular density, mucopolysaccharide or collagen compositions between groups 1 and 2 (p > 0.05). In addition, when groups 1 and 2 were compared with the control group, there was a significant decrease in goblet cells (p < 0.001), an increase in acute inflammatory cells, chronic inflammatory cells, fibroblasts, epithelial thickness and vascular density (p < 0.001), but there was no significant difference in mucopolysaccharide and collagen compositions (p > 0.05). Conclusions: This study suggests that at the time of surgery a high number of goblet cells may be a predictor of lowered IOP (less than or equal to 16 mm Hg) following trabeculectomy without antimetabolite. Copyright (C) 1999 S. Karger AG, Basel.