In 6,211 live-born infants born to mothers of low socioeconomic status, approximately one half received routine care, one quarter were held for evaluation, and one quarter manifested morbidity (illness or malformation). In term infants morbidity was low, but the number of sick infants was high; the reverse was true of low-birth-weight infants. Morbidity-to-death ratios were 37:1 in term infants, and 5:1 in low-birth-weight infants. Ten percent of survivors had a known problem at discharge. To permit the rapid application of present knowledge, changes in philosophy of nursery care are necessary. Traditional nurseries operate on the assumption that newborn infants are healthy until proved ill. A nursery functioning on the assumption that all newly born infants are potentially ill until good health is demonstrated may offer advantages.