The objective of the present study was to assess whether the influences of gender, age, or measures of body size on blood pressure are homogeneous among genotypes of the insertion/deletion (I/D) polymorphism of the gene that codes for angiotensin-converting enzyme (ACE). We studied a sample of 1875 non-Hispanic white individuals (988 female and 887 male subjects) between 5 and 90 years of age from the general population of Rochester, Minn. When statistical interactions between effects associated with the I/D polymorphism and age, height, and weight were not considered, there was no evidence of a significant relationship between variation in blood pressure level or diagnostic category (hypertension versus normotension) and variation in ACE genotype in either gender. However, in females 5 to 29.9 years of age, the linear regression relationships of systolic blood pressure level with age and weight and of diastolic blood pressure level with age were significantly heterogeneous among ACE genotypes. For these concomitant traits, the rank order of expected blood pressure levels associated with each genotype reversed from low values of the concomitant, in which blood pressure was lower for I/D heterozygotes than for II or DD homozygous, to high levels of the concomitant, in which blood pressure was higher for I/D heterozygotes than for II or DD homozygotes. In male subjects 50 to 90 years of age, the logistic regression relationship of the probability of having hypertension with height was also heterogeneous among ACE genotypes; it was statistically significant in II homozygotes but not statistically significant in either I/D heterozygotes or DD homozygotes. Findings of this study are consistent with the conclusion that the influence of variation in the ACE gene on interindividual variation in blood pressure is dependent on contexts that are indexed by gender, age, and measures of body size.