Proliferation and migration of lens epithelial cells is at the origin of after-cataract, currently the main side effect of cataract surgery. Extracapsular cataract surgery necessitates opening of the anterior lens capsule and removal of the lens fibres before an intraocular lens can be placed in the cleaned capsular bag. The present study was aimed at testing the potential of the lens capsule and the fibres to affect the mitotic activity of the lens epithelial cells in human donor eyes. Pairs of human lenses used in this study were subjected to two different experimental conditions. In the first, only a small anterior capsulorhexis was made. In the other, fibres were separated from the epithelium by gentle hydrodissection, the nucleus was rotated and, either left in the capsular bag or removed by hydroexpression. The specimens were cultured for 48 hr in MEM with 2% serum. Mitotic activity was assessed by immunohistochemistry using the bromodeoxyuridine (BrdU) incorporation technique. Fellow lenses of the same donors were cultured intact as controls. Anterior capsulorhexis showed a small but significant (P < 0.02) increase in the number of BrdU positive nuclei in the equatorial region but not in the wound area. Lenses where fibres were separated from the epithelium showed a large increase in BrdU incorporation in the germinative region, as compared to the intact control lenses (P < 0.01). BrdU incorporation was highest when fibres were removed. Lens capsule integrity and the presence of contacts between fibres and epithelial cells may have a role in the control of the mitotic activity of the lens epithelium. The data recorded here could be useful for understanding lens cell biology and prevention of after-cataract.