Palacos bone cement with and without contained gentamicin was tested for antibacterial efficacy using a rabbit model of a knee hemiarthroplasty and a challenge with intra-articular Escherichia coli. The gentamicin-containing cement prevented infection from challenge with Escherichia coli and protected against inadvertent operative infection as well. Antibiotic concentrations in synovial fluid and urine remained in the therapeutic range for three days, whereas levels in serum were always quite low. Eight per cent of the gentamicin had leached out of the bone cement by eight days, most of it during the first day. Thereafter, extremely small amounts of gentamicin left the cement on a daily basis. The amount of antibiotic leaching out in vitro was proportional to the surface area of the cement. More eluted into serum than into saline.