The amounts of interleukin-1 beta (IL-1 beta) (by enzyme linked immunosorbent assay (ELISA) using anti-rabbit recombinant IL-1 beta (rIL-1 beta) antibody) and total protein content (by Bradford's method) were assayed in the aphakic and pseudophakic aqueous humor in 24 eyes of 16 rabbits. Posterior chamber intraocular lenses were examined scanning electron microscopically and immunohistochemically. The amount of detected IL-1 beta was 10.79 +/- 4.67 ng/ml (mean +/- SD) in the pseudophakic eyes 3 days postoperatively, 10.12 +/- 3.96 ng/ml in the pseudophakic eyes and 3.94 +/- 0.86 ng/ml in the aphakic eyes 7 days postoperatively. A significantly higher amounts (p less than 0.001) of IL-1 beta were detected in the pseudophakic eyes compared with the aphakic eyes at 7 days postoperatively. The amount of IL-1 beta varied in each rabbit 1 month postoperatively. In total protein content in the aqueous humor, pseudophakic eyes showed significantly higher compared with the aphakic eyes at 7 days (pseudophakic eyes: 29.7 +/- 11.7 mg/ml, aphakic eyes: 8.58 +/- 6.90 mg/ml, p less than 0.05) and 1 month (pseudophakic eyes: 8.30 +/- 1.21 mg/ml, aphakic eyes: 2.10 +/- 0.309 mg/ml, p less than 0.001) postoperative. Scanning electron microscopic study showed that small round cells, spindle-shaped cells and giant cells could be observed on the surface of intraocular lenses. All of these types of cells showed positive staining of IL-1 beta immunohistochemically. These results suggest that IL-1 beta might be an inflammatory mediator in eyes with lens extraction, especially pseudophakic eyes.