1. The gene for dipeptidyl carboxypeptidase 1 (angiotensin I-converting enzyme, kininase II; DCP1), located on chromosome 17q23, has been implicated in hypertension in rats. In humans associations have been found for the insertion allele of a bi-allelic insertion/deletion polymorphism of DCP1 with hypertension and the deletion allele with myocardial infarction. Other hypertension studies have, however, failed to find a relationship. 2. Mathematical predictions based on DCP1 association data suggest that high sib-pair numbers may be needed to achieve statistical significance by this approach, although differences in the severity of hypertension in different study groups could account for the disparate findings. 3. No association was found between DCP1 allele or genotype frequencies and obesity in essential hypertensives.