This study was designed to examine the effects of rapid eye movement (REM) sleep deprivation and stress on the properties of peripheral benzodiazepine receptors (PBRs). Rats were deprived of REM sleep for 96 hours by a small pedestal (water tank) method. Using radioligand assays with the selective antagonist [3H]PK11195, receptor density (Bmax) and affinity were measured in the heart and kidney in three groups: 1) REMSD group (REM sleep deprived-group), 2) TC group (tank control group; large pedestal), and 3) CC group (cage control group). REMSD group showed an increase in the density of PBRs in the heart (18%; p<0.002), but not in the kidney (-5%; p=0.058) compared to TC group, and IC group showed an increase in the density of these receptors in the heart (17%; p<0.014), and the kidney (12%; p<0.002) compared to CC group. While the cardiac Kd value was 37% (p<0.0004) and 36% (p<0.002) higher in the REMSD group than in the CC and TC groups, respectively, the renal Kd value was lower (-5%; p=0.057 and -16%; p<0.0004, respectively). The changes in PBRs observed herein are tissue- and treatment-specific, and may suggest a close functional relationship between REM sleep and PBRs.