Concentrations of estradiol, progesterone, 17OH-progesterone were measured by radioimmunoassay in individual serum samples obtained from a group of 304 women with normal gestations between the 4th and 17th week of pregnancy. Values obtained underwent statistical analysis in order to determine the arithmetic mean and the 95% normal range (+/- two standard deviations). It was noted hereby that the spread of values above the mean was greater than that below the mean, and that very often the mean minus two standard deviations was either close to zero or negative. Therefore, the data for each hormone were analyzed for normality of the distributions by the chi-square test. For each hormone the chi-square test was significantly different (p less than 0.001) from the normal distribution (Gaussian). Subsequently, linear transformation by rankit analysis revealed the log-normal distribution of our data. Furthermore, rankit analysis was used as a graphical method to delineate a useful clinical range, which includes the mean and meaningful 95% confidence limits for estradiol, progesterone, and 17OH-progesterone in early normal pregnancies.