in vivo passage of albumin from the aqueous humor into the lens purpose to determine if albumin the major protein component of the aqueous humor passes into the lens in vivomethods rat albumin was covalentlylabeled with alexa 488 fluorophore purified by gel permeation chromatography then injected into the aqueous chamber of living rats at 5 min postinjection lenses were removed and analyzed by hplc gel permeation chromatography confocal microscopy and immunogold electron microscopyresults at 5 min postinjection hplc analysis detected measurable amounts of alexalabeled albumin in the lens the results were confirmed by confocal microscopy which showed passage into epithelial and cortical fiber cells immunogold electron microscopy using antibody to the alexa fluorophore demonstrated intracellular location of the alexaalbumin complexconclusions in vivo significant amounts of albumin pass from the aqueous chamber into cells of the lens consistent with a possible physiological role for this process involving passage of metabolites into the lens