Energy content offormula milk made up from powder by 19 mothers (expected value is 68 kcal/100 ml (284 kJO/100 ml)) Average

(kcal/100 ml)

Minimum (kcal/I00 ml)

Maximum (kcal/100 ml)

47

81 73 67 77 91 76 67 80 74 84 74 75 80 76 82 84 80 81 85

59 62 63

49

57 43 53 47 65 41

65 66 66 67 67 69 69 70 71 73 74 76 76 76 77 82

64 46 60 67

67 72 66 69 72 71 76

ment for potassium in tap water. The table shows mean, minimum, and maximum values for each subject. Minimum energy contents were often very low; one third were under 50 kcal (209 kJ) per 100 ml and the lowest only 41 kcal (171 kJ) per 100 ml. Maximum values were often far too high; about a half were over 80 kcal (334 kJ) per 100 ml-the highest was 91 kcal (380 kJ), 34% above the manufacturers' intended value. Under half the mothers consistently made up milk with less than 20% error and only two with less than 10% error. In 8 of the 19 subjects the mean energy content for the whole series of samples from each mother lay outside the range currently recommended by the Department of Health, 65-75 kcal (272-314 kJ) per 100 ml of formula. Mothers were increasingly likely to make up overstrength feeds with increasing time post partum; the first samples taken from each mother averaged 67 (SE 2) kcal (280 (SE 8) kJ) per 100 ml, rising to 73 (1) kcal (305 (4) kJ) per 100 ml by the third sample (p