Retinal pigment epithelial (RPE) cells of the vertebrate eye contain melanin packaged in structures called melanosomes. Previously, we reported that the bovine melanosome has a laser photodisruption threshold of 153.6 mJ/cm2 at 25°C and 532 nm, and an internal absorption coefficient of 2237 cm-1. Those values used an estimate of melanosome density inferred from studies of skin laser effects. We now revisit that calculation using a density value obtained from density centrifugation analysis of bovine and baboon RPE melanosomes. Stepped-density gradients (60% to 80%) of the nonionic medium, Nycodenz, were formed, and samples of melanosomes were spun on the gradients in a swinging-bucket rotor at 10,000 rpm for 60 m. Bovine melanosomes formed two populations, one at the interface between 70% and 75%, and the other between 75% and 80%, corresponding to the densities of ~1.38 and ~1.41 gm/cm3, respectively. Baboon melanosomes migrated to within the same density region. Using a density value of 1.41 gm/cm3, and assuming a water content of 52% for hydrated melanosomes, the internal absorption coefficient was calculated as 2339 cm-1. Although this calculation uses an objective density measurement, the water content remains an estimate, and the actual value in situ may differ.