ExtractTwenty-six infants weighing less than 1,300 g at birth were divided into pairs according to birth weight (900–1,100 and 1,101–1,300 g) and gestational age (“appropriate” (AGA) = mean 31 weeks; and “small” (SGA) = mean 34 weeks). One member of the pairs was then allocated randomly to one of two treatment regimens with oral sodium bicarbonate.Group Awas treated whenever base excess was greater than −8 mEq/liter as detected on twice weekly testing and/or when suspected to be acidotic from failure to gain weight. Ingroup B, base excess was maintained within 1 SD of normal (-3.2 ± 1.7 mEq/liter). The infants received Enfalac 200 ml/kg/24 hr, at 67 cal/100 ml, with vitamin D 400 IU/24 hr added from age 2 weeks.The following measurements were made: daily weight, weekly length, skinfold thickness, head circumference, twice weekly blood pH, PaCO2, base excess, and weekly plasma total calcium, ionic calcium, total magnesium, inorganic phosphorus, and total protein.There were six pairs each of AGA and SGA infants and two unpairedgroup Ainfants. Weekly weight gains did not differ betweengroup Aandgroup Bor between AGA and SGA. Length increment was greater in AGA than in SGA babies (0.94 ± 0.02 us 0.85 ± 0.04 cm/week) but not significantly so (P< 0.1), and ingroup Bbabies compared togroup Ababies (0.973 ± 0.029 vs 0.83 ± 0.037 cm/week) (P< 0.01).Plasma pH was lower ingroup A(7.23 ± 0.02) than ingroup B(7.30 ± 0.02) and calcium ion activity higher (group A2.72 ± 0.04;group B2.51 ±0.06 mEq/liter) between ages 20 and 29 days. Plasma magnesium was higher ingroup A(1.77 ± 0.04 mEq/liter) than ingroup B(1.56 ± 0.06 mEq/liter) from age 20 to 39 days. Inorganic phosphorus concentrations were consistently higher ingroup Athan ingroup B, but the differences did not reach significance. Mean total protein concentrations did not rise above 4.5 g/100 ml and tended to be higher in babies ofgroup Athan ofgroup B.Bone age was retarded in all babies. Radiographs available for 7 of 13 SGA infants were normal, whereas 6 of 11 radiographs of AGA babies showed some osteoporotic changes.SpeculationCareful control of late metabolic acidosis in infants < 1.3 kg birth weight results in less ionic hypercalcemia and improved growth in length. In the more immature AGA infants, radiologic osteoporosis was seen. Mineral and protein content of formula currently used for feeding infants of less than 1,300 g birth weight is inappropriate to their requirements for growth.