Age-dependent changes of serum alpha-fetoprotein (AFP) levels were analyzed in 284 normal infants, including 113 full-term neonates and 171 infants between 1-12 months old. Serial statistical analyses attempted to clarify some confusing and conflicting observations presently existing in the literature. The results showed the following: (a) variations of AFP values were homogeneous throughout infancy, after the logarithmic transformation that is essential in dealing with AFP data. (b) To obtain an approximately 95% prediction band of normal AFP levels in infancy, the regression analysis should be based on the power regression rather than the exponential progression model: log Y = 7.397 - 2.622.log (X + 10), where X = age in days and Y = AFP level in nanograms per milliliter. (c) A sex-related difference existed with higher mean values for male babies between 2-4 days of age, a fact that may be missed with casual analysis. In addition, the mean AFP level was found to be relatively constant at some time during the 1st week of life, in contrast to its subsequent extremely rapid decline. These characteristic changes deserve further investigation.