Fifty normal human placentae from various gestations were analyzed for total DNA, RNA, and protein content. The data indicate that, although weight, RNA, and protein continue to increase linearly until term, the rate of increase in DNA rapidly declines when the placenta reaches about 300 gm or the fetus 2,300 gm. When these data are interpreted in terms of number and size of cells they suggest that cell division stops in human placenta about 1 month prior to term. The latter portion of placental growth is by enlargement of already existing cells. These data establish normal values for human placenta from 26 through 42 weeks and provide a base line to compare placentae of abnormal pregnancies.