Chronic osteomyelitis is refractory because of the characteristics of bone. The soft tissues of bone are surrounded by hard walls, and inflammation of the contained tissues causes circulatory disturbances which can readily read to necrosis of various parts of the bone. Since it is impractical to deliver antibiotics to the target tissue at a sufficiently high concentration by the intravenous route, local administration is considered to be essential. There are many materials for drug delivery system. Antibiotic-containing cement beads qualify as a drug delivery system. The distance to which the effective concentration of an antibiotic extends from the carrier material is of clinical importance in evaluating a drug delivery system. We evaluated the concentration of gentamicin released from gentamicin mixed bone cement in bone marrow and bactericidal activity of released gentamicin according to time. Female albino rats weighing approximately 350 grams were used. Beads were made to gentamicin mixed Palacos PMMA bone cement. Three rats in each group were killed on 1st, 3rd day and 1st, 2nd, 3rd, 4th, 5th and 6th week. Extracted bone marrow was homogenized with 5ml of phosphate buffer saline (PBS) and removed beads with 5ml of PBS were incubated for 24 hours in 37degrees C. Gentamicin concentration from bone marrow and elution fluid from removed bead was measured using TDX machine and bactericidal activity of released gentamicin was measured by bactericidal broth dilution method using Bacillus subtilis ATCC 21008. Gentamicin sulfate gave a maximum concentration within the 1st week, which gradually decreased but was still effective at 6th week. Gentamicin concentration from removed bead gave a maximum concentration at 1st day, which gradually decreased to 6th week.