Hypertonic saline, when injected into the lumbar subarachnoid space for the relief of intractable pain, causes pain, unpleasant muscle cramps and potentially dangerous sympathetic discharge. These side effects can be avoided by adding a weak concentration of local anaesthetic to the brine solution. Fourteen intrathecal injections of 8 per cent sodium chloride and 0.4 per cent lidocaine (osmolality: 2788 m.Osmols/Kg) were made in 9 patients. Serial measurements of cerebrospinal fluid osmolality and chloride content were made during the succeeding 15 minutes. Cerebrospinal fluid osmolality increased four to eight-fold shortly after injection, and was still three to six times higher than normal 15 minutes later. The procedure was painless, and free of cardiovascular disturbances.