This study examined the cardiovascular, renal, and hormonal responses of dietary-induced obesity in Osborne-Mendel (OM) rats. Male OM rats were fed either a low (LF; n = 10)- or high-fat (HF; n = 11) diet for 17 wk. During week 15 of the study, arterial pressure was measured directly, 24 h/day, from chronically indwelling catheters. Body and kidney weights were 46 +/- 5 and 33 +/- 5% greater, respectively, in rats fed HF vs. LF diet. Left and right ventricular weights were also greater in rats fed HF diet (21 +/- 7 and 36 +/- 6%, respectively). Direct measurement of arterial pressure revealed only a slight increase in mean arterial pressure (88 +/- 1 in rats fed HF diet vs. 85 +/- 1 mmHg in rats fed LF diet), whereas there was no difference in resting heart rate between the two groups. Consumption of HF diet was also associated with a 3.5-fold increase in plasma insulin, a 16 +/- 4% higher blood glucose, and a 40 +/- 6% reduction in plasma renin activity compared with LF-fed rats. Thus feeding OM rats HF diet led to obesity, cardiac and renal hypertrophy, and hyperinsulinemia but only a slight increase in mean arterial pressure.