Polybutylcyanoacrylate nanoparticles of 3H labelled gentamicin were used to investigate the possibility of gentamicin nanoparticles as the drug delivery system for intracellular chemotherapy. 3H labelled gentamicin nanoparticles were incubated with mouse peritoneal macrophages or rat hepatocytes for various lengths of time. The cells were then separated from the nanoparticles and the radioactivity of 3H in the cells was measured by a liquid scintillation counter. By comparison with the gentamicin solution, the binding to nanoparticles produced a 5.34-fold increase in the uptake of gentamicin by the macrophages in 30-min incubation and 26.74-, 8.03-and 7.36-fold increase in uptake by the hepatocytes in 1-, 12-and 24-h incubation. The stabilizers used in the preparation of nanoparticles, particle size, surfactant coating and the gentamicin concentration were each found to have an effect on the uptake of the nanoparticles by both types of cells.