SUMMARY After subcutaneous injection in oil or saline the incorporation patterns of tritiated oestradiol and oestrone were studied in tissues classically regarded as reactive and non-reactive to oestrogens. The former incorporate far more activity than the non-reactive tissues. Incorporation of oestradiol and oestrone after injection in oil showed a similar pattern, although the uterus and vagina incorporated four times as much oestradiol as oestrone. Uptake from saline was more rapid with both compounds. The pattern with oestradiol injected in saline was similar to that with injection in oil, whereas with oestrone levels were high and declined from the earliest time studied.