Ischemia is considered to invalidate the estrogen receptor (ER) and progesterone receptor (PR) values of tissues available for steroid hormonal analysis. To evaluate the temporal effect of devascularization on steroid receptors, complete uterine ischemia was induced in vivo in 64 female Buffalo rats (80-154 g). Animals were assigned to varying intervals of ischemia (0-90 min) and were maintained at a constant ambient (75°F) and core-body temperature (100-102°F). Following tissue preservation at -80°C, multipoint titration of steroid binding capacity (SBC) was performed with [3H]estradiol 17-β (3-0.15 nM) or [3H]R5020 (8-0.4 nM) in the presence or absence of a 200-fold excess of an unlabeled ligand. Applying nonlinear regression analysis, ischemia was observed to decrease the binding capacitance for both ER and PR profiles of rodent uterine tissues at 30 min with significant decay over the 90-min interval of devascularization (ER, P < 0.01; PR, P < 0.1). Significant reduction in SBC was evident after 80 min of ischemia for PR (P < 0.05) and 90 min of tissue ischemia for ER (P < 0.05) comparative to control (t0) valves. The detrimental effect of progressive ischemia on ER and PR values was such that it appears essential to assure rapid and reliable tissue aliquot preservation techniques when organ ischemia ≥ 90 min is anticipated. © 1987.