IN an earlier communication1 attention was directed to the transfer of metal which can occur between a screwdriver tip and a screw head during the operation of screwing, and the possible significance this might have in orthopaedic surgery was discussed. It was demonstrated by a radioactive tracer method that, whenever a screw is inserted, small fragments of metal are plucked out of the driver and remain adhering to the screw head. It was suggested that, although the amount of metal transferred is very small (about 10–100 µgm.), the particles may form corrosion centres and cause metal ions to pass into the surrounding tissue. This may cause tissue reaction and interfere with normal physiology even in cases where no gross corrosion is observed.