Data from a long-term, open-label diltiazem trial were analyzed to test the hypothesis that the magnitude of systolic blood pressure (SBP) response to diltiazem is dependent on pretreatment levels. The study design included a 2- to 4-week placebo period to establish stable qualifying pressures. Patients devoid of significant coexisting diseases with diastolic blood pressures (DBPs) greater than or equal to 95 mm Hg or SBPs greater than or equal to 160 mm Hg were titrated on sustained-release diltiazem (60-180 mg b.i.d.) over 2-6 weeks. Titration goals were greater than or equal to 10% drop in DBP or greater than or equal to 15% in SBP. Patients were followed up to 20 months. Based on pretreatment blood pressure, patients were divided into three subgroups: isolated systolic hypertension (ISH) (SBP/DBP; greater than or equal to 160/less than 95 mm Hg), isolated diastolic hypertension (IDH) (less than 160/greater than or equal to 95 mm Hg), and combined systolic and diastolic hypertension (CSDH) (greater than or equal to 160/ greater than or equal to 95 mm Hg). SBP changed significantly from baseline for all three groups. However, the percent reduction in SBP was significantly greater for patients with baseline SBP greater than or equal to 160 mm Hg when compared with patients with baseline SBP less than 160 mm Hg (-10.3 +/- 0.7% vs. -4.4 +/- 0.6%). In comparing the ISH and CSDH patient groups, the CSDH group required a larger diltiazem dose to achieve a SBP response similar to the ISH group. Diltiazem was well tolerated with only a 5% dropout due to adverse effects of therapy.(ABSTRACT TRUNCATED AT 250 WORDS)