Evidence is presented demonstrating that in the dogfish, Squalus acanthias, D-glucose is transported from the blood to the ocular fluid compartments by a mechanism that is consistent with carrier-facilitated transport. Across the dogfish aqueous barrier D-glucose is transported 8.4 times faster than L-glucose, whereas this D/L transport ratio is only 5.5 in the rat. Similarly, the D/L transport ratio is 12.7 across the dogfish vitreous barrier and only 6.1 across this barrier in the rat. It is estimated that per unit area of vitreous barrier, the rat transports D-glucose faster than the dogfish but also has a greater passive permeability, as measured by L-glucose, and transport is therefore less efficient. Urea transport was found to be faster than L-glucose transport, suggesting a transport mechanism for urea other than simple diffusion. The sectional analysis of frozen vitreous humor indicated that the lens of the dogfish is supplied with D-glucose from both the ciliary epithelium and across the retinal pigment epithelium, while the retina receives D-glucose primarily across the pigment epithelium.