In 6 rabbits with 38 fetus

the pH 6.5 and 9.6 preparations with the same dosage of rivanol given to uterine cavity for 6 hours were studied to diffuse into fetus. The same volume amniotic fluid was withdrawn from every fetus and determined for rivanol contents. The amount of pH 6.5 and 9.6 rivanol preparation diffused into every fetus are (X±SD) 0.18±0.07 and 0.065±0.04ug (P<0.01) respectively. The pH 6.5 preparation of rivanol into fetus is more readily than the pH 9.6 preparation.