Blood levels of iron, transferrin and ferritin varied in the course of pregnancy (6th to 42nd week) in 136 women. Analysis of variance showed that the factor “weeks of pregnancy” (< or = 27 or > 27 weeks) was correlated differently with the variables “ferritin” and “iron” according to the presence or absence of anemia (Hb < or = or > or = 11 g/dL). In anemic women the correlation was significant (F-ratio = 5.90; P = 0.018) for iron (which decreased from initial low level until term) but not ferritin, whereas in non-anemic women the correlation was significant (F-ratio = 13.306; P = 0.0006) for ferritin (which decreased to less than 20 micrograms/ml around the 34th week) but not iron. In both anemic and non anemic subjects, transferrin levels increased with weeks of pregnancy. It is concluded that towards the end of pregnancy, some decrease in ferritin (> or = 15 micrograms/ml) is physiological, and in the absence of anemia (Hb > 11 g/dl) iron supplements are not necessary.