The in vivo release of gentamicin base from conventional polymethyl methacrylate 7-mm beads was compared with that from the recently introduced 3 × 5-mm minibeads. The release in 14 days from minibeads was 93 percent of their gentamicin content, while the large beads released an average of 24 percent. The volume of the minibeads is one fifth of that of the large beads, Owing to the improved release combined with the smaller size, total release from minibeads in a cavity may be some seven times that from large beads. When in smaller cavities a strong bactericidal effect is desired, minibeads are to be preferred to large beads.