PURPOSE: To investigate the in vitro toxicity of indocyanine green and infracyanine green (ICG) to cultured ARPE19 cells, in particular with respect to the concentration and time dependence of this toxicity. METHODS: ARPE19 cells were grown for at least 1 week past confluence (hyperconfluent cells) before being subjected to challenge with ICG. Cell survival was tested with the MTT assay. RESULTS: When applied in isotonic solutions, ICG in all concentrations (below 5 mg/ml) and at all exposure times tested (2 mins-2 hours) was found not to affect the survival of ARPE19 cells. ARPE19 cultures older than 30 days were more resistant to a 5 mg/ml hypotonic ICG solution than younger cultures. CONCLUSION: When toxicity of ICG was tested in hyperconfluent ARPE19 cultures, these cells were found to be more resistant to the dye than has been previously reported for more immature ARPE19 cells.