METHODS: The association of blood pressure (BP) with the beta-adducin C1797 T polymorphism was investigated in 388 men and 456 women aged 18-60 years recruited from three European populations (Cracow, Poland, n=300; Novosibirsk, Russian Federation, n=274; Mirano, Italy; n=270). Phenotypes included conventional measurements of BP obtained at the second contact with the subjects and 24-h ambulatory BP. Subjects were genotyped for the beta-adducin C1797 T polymorphism. Both a population-based association study and a family-based analysis were performed. RESULTS: Urinary sodium excretion was higher in Cracow than in Mirano (241 versus 185 mmol/day, P<0.05) and intermediate in Novosibirsk (206 mmol/day). The beta-adducin T allele (15.2 versus 9.1%, P<0.0001) was more prevalent in Mirano than in the two Slavic centres. In both population-based and family-based association analyses, there was significant heterogeneity between Slavic and Italian subjects in the phenotype-genotype relationships with beta-adducin. Adjusted population-based analyses demonstrated that in the two Slavic centres, values of systolic pressure obtained by 24-h, daytime and night-time ambulatory monitoring, but not those measured by conventional sphygmomanometry at home, were significantly higher in T allele carriers than in CC homozygotes. These results were confirmed in the family-based analysis of offspring using a quantitative transmission disequilibrium test. CONCLUSIONS: Phenotype-genotype associations involving blood pressure are influenced by the technique and conditions of the BP measurement as well as by the overall ecogenetic context.