['The family kitchen resembles an uncontrolled laboratory experiment, and some discrepancies in the relation between the risk of hypertension and dietary fat may be partly due to the manipulation to which the fats were subjected.', 'We investigated whether deterioration in the quality of the cooking oils in the family household contributes to the risk of high blood pressure.', 'The study was cross-sectional. Anthropometric measurements were obtained for 1226 persons aged 18-65 y who were selected randomly from the municipal census of Pizarra, Spain. An oral-glucose-tolerance test was given to 1020 of these persons. Samples of the cooking oil being used were taken from the kitchens of a random subset of 538 persons. The concentrations of polar compounds and polymers were used as markers of the deterioration of the oils. The strength of association between variables was measured by calculating the odds ratio from logistic models.', 'Hypertension was strongly associated with obesity and was influenced by sex, diabetes, and age. The presence of excess polar compounds in the cooking oil and the use of sunflower oil were related to the risk of hypertension, whereas the concentration of monounsaturated fatty acids in the serum phospholipids was negatively related to this risk. These associations remained after inclusion in the models of age, sex, obesity, and the presence of carbohydrate metabolism disorder.'] Is hypertension related to the degradation of dietary frying oils?