A delivery system consisting of the lipophilic fluorescent dye coumarin-6 embedded into polymer nanoparticles in a suppository base was formulated. Particle diameters of 400-1100 nm were produced by a salting-out method and measured by laser diffraction. Nanoparticles reach the systemic circulation via fenestrated capillaries or remain within rectal membranes to release their contents. Dissolution over 168 hr was initially rapid followed by a steady decline, and tissue distribution showed coumarin-6 to be present in liver and lungs for a similar time period while in kidney, small intestines, and blood up to 96 hr. Microscopic observations showed nanoparticles to be present in blood up to 72 hr.