The sodium intake of preschool children in their home environment was investigated and the major sources of sodium other than added table salt identified. Thirty five children from a Southampton general practice were studied. Twenty four hour urinary sodium excretion was measured as a reliable indicator of daily total sodium intake. The daily intake of sodium other than that from added table salt, and of potassium and other nutrients, was also calculated from three day dietary diaries collected using the household measures method. Median excretion of sodium was 62 mmol/24h (range 28-105, 28 urine collections) and of potassium was 25 mmol/24 h (range 14-46). The sodium:potassium ratio was 2.7 (1.4-5.2). From the diaries, the average daily intake of sodium was 68 mmol (32-98) and of potassium was 47 mmol (24-95), and the sodium:potassium ratio was 1.4 (0.5-2.7) (median and ranges, 35 children). Foods contributing more than 30 mmol sodium to one day's intake were mainly processed convenience foods.