SUMMARY Recently introduced plastic swivel connectors (both autoclavable and disposable) were examined under laboratory conditions for gas leakage. The leak from the autoclavable connectors before autoclaving nearly always exceeded 5% Although this leak was diminished after autoclaving, the swivelling property was greatly decreased. The position of maximal leakage was found to vary with the position of the connector on the tracheal or tracheostomy tube adaptor. The magnitude of the leaks obtained varied, only the disposable connectors complying with our own criteria. Comparison of the plastic connectors was made with one type of metal swivel connector which was also found to be acceptable for clinical use.