This investigation was undertaken to study the clinical and histologic appearance of deciduous enamel from 11 infants who were subjected to blood exchange transfusions (ET) during the first days of life. As a result of the treatment they had a mean of 3 consecutive hypocalcemic days. At the age of 5 years a dental examination of their primary teeth was performed. Four of the children had clinically recorded enamel aberrations correlated with the neonatal period. Exfoliated teeth were then examined histologically. All had a normal major enamel morphology, and the neonatal line was present in all teeth. Histologically investigated teeth with enamel hypoplasia had the aberrations located close to the neonatal line. The conclusions drawn from this study are that hypocalcemia caused by ET in the newborn period did not affect the width of the neonatal line or the major enamel morphology to any extent. Enamel aberrations occurred only when four or more ETs were performed.