We report for the first time that cultured lens epithelial cell layers and rabbit lenses in vitro transport fluid. Layers of the αTN4 mouse cell line and bovine cell cultures were grown to confluence on permeable membrane inserts. Fluid movement across cultured layers and excised rabbit lenses was determined by volume clamp (37°C). Cultured layers transported fluid from their basal to their apical sides against a pressure head of 3 cmH₂O. Rates were (in μl ⋅ h⁻¹ ⋅ cm⁻²) 3.3 ± 0.3 for αTN4 cells (n = 27) and 4.7 ± 1.0 for bovine layers (n = 6). Quinidine, a blocker of K⁺ channels, andp-chloromercuribenzenesulfonate and HgCl₂, inhibitors of aquaporins, inhibited fluid transport. Rabbit lenses transported fluid from their anterior to their posterior sides against a 2.5-cmH₂O pressure head at 10.3 ± 0.62 μl ⋅ h⁻¹ ⋅ lens⁻¹(n = 5) and along the same pressure head at 12.5 ± 1.1 μl ⋅ h⁻¹ ⋅ lens⁻¹(n = 6). We calculate that this flow could wash the lens extracellular space by convection about once every 2 h and therefore might contribute to lens homeostasis and transparency.