Aims - To examine factors influencing the density and contact inhibition of bovine corneal endothelial cells cultured in vitro. Methods - Cell counts were performed on bovine corneal endothelial cells cultured for various times in the presence of 10% fetal calf serum, with or without varying concentrations of growth factors, 5% dextran T-500, or 2% chondroitin sulphate, at 32°C or 37°C, and after treatment with β galactosidase. Results - Both basic fibroblast growth factor (FGFb) and retinal crude extract (RCE), but neither epidermal growth factor (EGF) nor acidic fibroblast growth factor (FGFa), increased endothelial cell density in vitro (p < 0.05). Continuous exposure to RCE resulted in a higher cell density than did a 24 hour pulse (p < 0.01), and higher cell densities were achieved at 37°C than at 32°C (p < 0.0001). In the absence of RCE, dextran T-500 increased cell density modestly (p < 0.05); in the presence of RCE, the addition of dextran T-500 had no effect on final cell density, whereas chondroitin sulphate significantly decreased final cell density (p < 0.01). In the absence of exogenous growth factors, β galactosidase treatment resulted in a 50% increase in final cell density compared with controls (p < 0.0001). Conclusions - Bovine corneal endothelial cell growth can be augmented under conditions different from those used in corneal preservation systems. The final cell density in a confluent monolayer can be increased by treatment with β galactosidase, suggesting that corneal endothelial cells may be contact inhibited through a β galactosidase sensitive receptor system.