myo-Inositol concentrations in oviduct, ovary and uterus were many-fold those of blood serum during all four stages of the estrous cycle of the female rat. 2. Inositol concentration was higher in oviduct than in ovary or uterus and was lower in uterine fluid than in uterus. 3. Estrus uteri had higher inositol concentrations than uteri in other phases of the cycle. 4. In order to measure dynamic aspects of the distribution of inositol, the distribution of radioactivity among organs of the reproductive tract of mature female rats was measured 45 min after i.p. injection of [2-3H]myo-inositol. 5. These organs concentrated inositol from the blood, and the tissue radioactivity (expressed as dpm/mg wet wt of tissue) increased in the sequence: vagina less than cervix less than uterus less than ovary less than oviduct. 6. The uterus and ovary concentrated myo-inositol more strongly during proestrus than during metestrus, diestrus of estrus. 7. The contents of proestrus follicles were more highly radioactive than was the ovary itself, whereas proestrus uterine fluid was less radioactive than the uterine tissue.