The effect of exogenous oestrogen on blood flow and quantitative histology of the corpus luteum were studied in pseudopregnant rabbits. Pseudopregnancy was induced with human chorionic gonadotrophin and an oestradiol capsule was implanted on day 0 of pseudopregnancy. Regression of the corpus luteum was initiated in the mid-luteal phase by removal of the capsule. Thirty-two New Zealand white rabbits were randomly allocated to four groups (eight rabbits per group) for studies of blood flow--control: oestradiol capsule not removed: -24 h: oestradiol capsule removed 24 h before blood flow measurements; -48 h: oestradiol capsule removed for 48 h; and -48 h/+48 h: oestradiol capsule removed for 48 h and then reimplanted for an additional 48 h. All blood flow studies were performed on day 11 of pseudopregnancy with radioactive microspheres. Quantitative histology was performed on a separate group of 16 rabbits allocated to the same groups as above (four rabbits per group). Blood flow to the corpus luteum was unchanged in the -24 h group, but declined by 44% in the -48 h group. Blood flow returned to control values in the -48 h/+48 h group. Quantitative histology revealed no changes in the -24 h group, but a significant decrease in volume of the corpus luteum and volume of the luteal cell cytoplasm in the -48 h group. Corpus luteum volume was fully restored and luteal cell cytoplasm volume was partially restored in the -48 h/+48 h group. In contrast, the number of luteal cells, vessel space volume and capillary surface area did not change with oestrogen withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)