There are inconsistent reports that the angiotensinogen (ATG) variant Met²³⁵→Thr (T235) allele and angiotensin-converting enzyme (ACE) insertion/deletion (I/D) variants are associated with hypertension and related target organ damage. Both high blood pressure (BP) and abnormal diurnal BP variation patterns are related to target organ damage, but it is not known whether the above genetic variants of the renin-angiotensin system are related to 24h BP and the diurnal BP pattern in Japanese. We studied the association of the ATG T235 allele and ACE D allele with 24h BP and diurnal BP variation in 235 of 262 consecutive untreated (or off medication) elderly Japanese hypertensives who underwent 24h ambulatory BP monitoring. There was no significant association between the T235 or ACE D allele with office BP, but the T235 allele was significantly associated with 24h BP and day BP, and the D allele was significantly associated with increased 24h BP, day BP, and night BP. There were no effects of the T235 or D alleles on any BP parameters. Those with white-coat hypertension had a significantly lower T235 allele frequency (0.68) than those with sustained hypertension (0.79, p=0.010), but the difference in D allele frequency was marginal (0.30 vs. 0.38, p=0.057). In conclusion, in elderly Japanese hypertensive individuals, both the ATG T235 and ACE D alleles are associated with increased 24h BP and day BP, while only the ACE D allele is associated with increased night BP. (Hypertens Res 1999; 22: 95-103)