The safety and efficacy of prolonged infusion of alphaxalonelalphadolone (Aljathesin: Glaxo) was assessed in 20 critically ill patients needing sedation during intermittent positive pressure ventilation in a general intensive care unit. The mean dose of Aljathesin infused was 1542 ml (range: 225 to 4820 ml) over 6.9 days (3 to 16 days) at rates between 5 and 15 mllhour. Significant increases in plasma urea, creatinine, bilirubin, alkaline phosphatase and white cell count occurred during the infusion, but these were expected from each patient's clinical course. Lipoprotein electrophoresis invariably showed loss of the alpha band and appearance of a densely staining prebeta band. Four patients had involuntary movements during the infusion and two patients fitted when the infusion stopped. Both had cerebral injuries. Subjective assessment of the quality of sedation was "very good" or "good" in 15 patients and "fair" in five.