An investigation of restriction fragment length polymorphisms (RFLPs) and association with blood pressure was carried out for the candidate genes coding for renin (REN) and atrial natriuretic peptide (ANP). The relationship between blood pressure, REN and ANP gene RFLPs was tested in a population of black Afro-Caribbean and white European subjects sampled randomly from family practice registers. Upper and lower quintiles for diastolic blood pressure were selected for analysis. Digests of DNA were prepared from leucocytes and RFLPs were determined using Southern blotting analysis with REN and ANP gene probes. There were highly significant ethnic differences found for BglI, Bg/lI and TaqI polymorphisms with 5'REN probe and for BglI polymorphism with an ANP probe. There was also an association between blood pressure and the BglI/REN polymorphism in Afro-Caribbeans but not with any other polymorphisms studied in either ethnic group. The findings show significant ethnic RFLP differences at the gene loci for both renin and ANP and provide evidence for a possible link between variations within or close to the renin gene and elevated blood pressure in Afro-Caribbeans.