We investigated the difference between male and female rats in the increase in blood pressure (BP) when they were fed a lard-enriched diet. We also investigated the effect of a gonadectomy, with or without testosterone treatment, on the dietary lard-induced increase in BP. Wistar-strain male or female rats were bilaterally castrated or ovariectomized. Some of them were implanted subcutaneously with silicon tubes containing crystalline testosterone. Each group was fed either chow alone or chow in which 50% of the energy content was from substituted lard. Systolic blood pressure (SBP) was determined weekly during each 7- or 11-week feeding period. A steady-state plasma glucose method was used to determine the insulin sensitivity. The dietary lard-induced increase in SBP was observed at 5 weeks after the start of the feeding in the sham-operated male rats. In the sham-operated female rats, SBP did not change from the basal values until 11 weeks into the experimental period. Castration eliminated the dietary lard-induced increase in SBP. Ovariectomy had no effect on SBP throughout the experimental period in both diet groups. In castrated males given testosterone, SBP increased in a dose-dependent manner. In ovariectomized females given testosterone, SBP increased significantly in the lard-enriched diet group. The dietary lard developed an insulin resistance in both the sham-operated and gonadectomized rats. However, SBP increased only in the sham-operated male rats. These results suggest that the dietary lard-induced increase in SBP depends on the presence of testosterone. The development of insulin resistance by dietary lard triggers the increase in SBP.