Objective To investigate the ingestion, metabolism and subcellular localization of indocyanine green (ICG) in human retinal epithelial (R PE) cells.Methods RPE cells were incubated with 0.25 mg/ml ICG under the condition of 37oC in the camera. The ICG granule and ultrastructure of RPE cells were observed under the electron microscopy after 1, 4, and 24hour incubation, and the ICG autofluorescence was detected by fluorescence microscopy after the incubation for 1, 2, 4, 8, 12, 24, and 48 hours, respectively. The ab sorbency (A value) of ICG solution was measured at 805 nm with ultraviol et/v isible specrtrometer. The standard curve of concentration of ICG was drawn and the related equation of concentration of ICG and the A value was calculated. After being incubated for 1, 2, 4, 8, 12, 24, 48, and 72 hours, respectively, the A value of supernatant fluid was calculated according to the equation. Aft er incubated with ICG for 24 hours, one sample was observed under electron microscope and fluorescence microscope per week to evaluate the metabolizable period of ICG .Results ICG granules were distributed evenly after entering the RPE cells. After incubated with 0.25 mg/ml ICG for 24 hours, no significant change of the ultrastructure of the RPE cells was found. ICG granules accu mulated in the cells as the time goes by and reached the peak after 24 hours, and then they decreased because of the slowdown of the metabolism. Few ICG was still remained in the cells 1 week later Conclusions RPE cells may take in ICG actively. ICG metabolizable period in RPE cells is long, which may be one of the mechanisms of the toxicity of ICG to the retina in the vitreous operation.(Chin J Ocul Fundus Dis，2004，20：179-181)