Solubility of fluroxene was determined in various media. Partition coefficients at 37°C. were: water/gas 0.84, blood/gas 1.37, olive oil/gas 47.7, cerebral grey or white matter/gas 1.96, liver/gas 1.88, and muscle/gas 3.11. Reduction in temperature increased solubility in both water and oil by 5 per cent per degree centigrade. The solubilities obtained correlate well with the clinical finding that fluroxene is a potent anesthetic with a rapid onset of anesthesia and recovery.