Changes in blood pressure during the first year of life were investigated in a one-year follow-up study. The blood pressures were measured at the age of one day from 245 newborns, at the age of four or five days from 224 infants, at the age of four months from 105 infants, and at the age of one year from 68 infants. Blood pressure increased considerably during the first five days. The increase of mean systolic blood pressure was markedly bigger, from 59 to 90 mmHg, than that of mean diastolic blood pressure, which was from 43 to 55 mmHg. The correlations of blood pressure were calculated with prenatal history, physical measurements and parental blood pressure. Significant correlations were found with physical factors but not with the prenatal history or parental blood pressure. The tracking of the blood pressure was not good. The distribution of the blood pressure values was normal. It is concluded that for the time being there are no reliable predictive factors to hypertension which could be found in early infancy.