We present a case of accidental injection of oral methadone and flunitrazepam into the ulnar artery, with resultant severe ischaemia of the hand. Initial therapy consisted of systemic vasodilators, low molecular weight dextran and aspirin. When this therapy failed to produce improvement and amputation of the involved hand seemed inevitable, the patient was referred for hyperbaric oxygen (HBO) therapy. In spite of a 12 day delay in the initiation of HBO, the response was dramatic, with almost complete resolution of the ischaemic signs and symptoms. Intra-arterial injection, which is only rarely encountered in drug addicts, frequently results in severe ischaemia of an extremity, and carries with it a poor prognosis with currently accepted therapy. Given the presently reported experience and the known physiology of HBO, we conclude that HBO should be started early in the treatment of intra-arterial injection of drugs, and should also be considered following prolonged delays.