Leptin increases sympathetic activity, possibly contributing to hypertension in obese subjects. Hypertension increases cardiovascular mortality, with nighttime (sleep) blood pressure having a substantial prognostic value. We measured blood pressure in male leptin-deficient obese mice (ob/ob; n=7) and their lean wild-type littermates (+/+; n=11) during wakefulness, non-rapid-eye-movement sleep, and rapid-eye-movement sleep to investigate whether, in the absence of leptin, derangements of blood pressure are still associated with obesity and depend on the wake-sleep state. Mice were implanted with a telemetric pressure transducer and electrodes for discriminating wake-sleep states. Mean blood pressure was significantly higher in ob/ob than in +/+ mice during wakefulness (7.3+/-2.6 mm Hg) and non-rapid-eye-movement sleep (6.7+/-2.8 mm Hg) but not during rapid-eye-movement sleep (2.6+/-2.6 mm Hg). In ob/ob and +/+ mice, mean blood pressure was substantially higher during wakefulness than during non-rapid-eye-movement sleep. On passing from non-rapid-eye-movement sleep to rapid-eye-movement sleep, mean blood pressure decreased significantly in ob/ob but not in +/+ mice. The time spent during wakefulness was lower in ob/ob than in +/+ mice during the dark (active) period, whereas the opposite occurred during the light (rest) period. Consequently, mean blood pressure was significantly higher in ob/ob than in +/+ mice during the light (8.2+/-2.4 mm Hg) but not during the dark (3.0+/-2.9 mm Hg) period. These data suggest that, in the absence of leptin, obesity may entail hypertensive derangements of blood pressure, which are substantially modulated by the cardiovascular effects of the wake-sleep states.