Concentrations of total estriol, progesterone, cortisol, human placental lactogen and alpha-fetoprotein were measured in maternal venous plasma at regular intervals from the seventh week of pregnancy until term in a woman with an anencephalic fetus. Except for the first trimester, during which the values were in the lower normal range, the concentration of estriol was constantly subnormal. The "physiological" rise in cortisol levels was absent. Progesterone and HPL were both within the low normal range. The levels of alpha-fetoprotein were transiently raised during the 13th--25th weeks of pregnancy.