FITC-dextrans as fluorescence and electron microscopic tracers in studies on capillary and cell permeability of the CNS.

FITC-dextrans can be detected at the ultrastructural level as round electron dense particles, with no sign of distortion or aggregation. Because this tracer is a stable, non-toxic polymer of biological origin obtainable in a wide range of molecular weights, it may be useful for further studies of tissue permeability.