We investigated whether hypertriglyceridemia and hyperleptinemia are involved in the development of increases in blood pressure induced by dietary lard. Rats received either chow alone or chow in which 50% of the energy content was from substituted lard. Each group was divided into two groups according to whether the diet included bezafibrate or not. In another series of experiments, rats were fed either chow alone or chow in which 50% of the energy content was from substituted lard, safflower oil, or sucrose. Systolic blood pressure (SBP) was measured every week during each 7-week feeding period. A steady-state plasma glucose method was used to determine insulin sensitivity after lard substitution with or without bezafibrate. After the 7-week feeding period, the plasma levels of glucose, immunoreactive insulin, triglyceride and leptin were measured. In rats fed with a high lard diet, SBP, plasma levels of immunoreactive insulin, triglyceride, leptin and steady-state plasma glucose concentrations significantly increased, compared with levels of these substances in controls. Bezafibrate treatment completely reversed these effects. In rats fed with a high safflower oil or a high sucrose diet, no significant change was seen in SBP and plasma immunoreactive insulin levels. However, the plasma triglyceride levels were increased by dietary lard or sucrose. Moreover, the plasma leptin level was also increased by dietary lard and safflower oil. Neither dietary hypertriglyceridemia nor hyperleptinemia were involved in the development of increases in blood pressure induced by dietary lard.