In vitro receptor autoradiography was performed on rat brain and kidney sections stored frozen at -20°C for extended time periods (17, 40, 64, 121, 183, 251, and 333 days). The results indicate that prolonged tissue storage has a differential effect upon125I sar1ile8 angiotensin II binding to AT1 and AT2 receptor sites. Binding at AT1 receptor rich tissues studied (renal medulla, renal cortex, anterior pituitary, ventral hippocampus, spinal trigeminal nucleus, and nucleus of the solitary tract) shows a first order exponential decay pattern. The logarithmic linear regression slope (log(e) specific binding versus time), is significantly different from zero (p<0.05) in all AT1 rich tissues except for nucleus of the solitary tract (p=0.086). There is no detected loss of 125I sar1ile8 angiotensin II binding at the AT2 prominent regions in the superior colliculus, medial geniculate nucleus, and the inferior olivary nucleus. The half lives of AT1 receptors are highly variable, ranging from 36 days in the anterior pituitary to 442 days in the nucleus of the solitary tract, and this might be related to variable stability of AT(1A) and AT(1B) receptors. These observations should be taken into account when assessing and comparing AT1 and AT2 receptor subtype densities.