A retrospective study was made of 17 severely burned patients with special reference to serum and urinary phosphate. A lowering of the serum phosphate level was regularly recorded between the 3rd and 9th day. The lowest mean value of serum phosphate of the group was 0.57 +/- 0.2 (S.D.) mmol/l (normal range 0.8-1.5 mmol/l) occurring on the 5th day after the accident. Serum phosphate then returned to normal levels in all the patients except three, who died. These three were among the four patients who showed the lowest serum phosphate values, less than 0.32 mmol/l, and their deaths coincided with the recording of these low values. The phosphate depletion seemed to be of prerenal origin. Hypophosphataemia may be of significance in the fatal outcome in some of the patients with severe burns.