A parallel-group, randomized, double-blind, forced-titration, multicenter study was done to compare the efficacy and safety of once-daily nifedipine coat-core (NIF CC) and once-daily nifedipine gastrointestinal therapeutic system (NIF GITS) dosed in the fasting state in patients with mild-to-moderate essential hypertension. Both formulations have been shown to effectively and safely lower blood pressure in placebo-controlled trials. After a 4-week placebo run-in period, 228 patients were randomized to 4 weeks of treatment with either NIF CC 30 mg daily or NIF GITS 30 mg daily. This period was followed by a forced-titration period to nifedipine 60 mg daily for an additional 4 weeks of double-blind therapy. After the 30-mg treatment period (the primary time point), there were no statistically significant differences between treatment groups in mean change from baseline in trough supine diastolic blood pressure, the primary efficacy variable (NIF CC patients, -7.0 mm Hg; NIF GITS patients, -8.4 mm Hg; P = 0.139). Also, because the upper bound of the treatment difference confidence interval was <3.0 mm Hg, equivalence-as defined in the protocol-was established. After the 60-mg treatment period, the change from baseline in trough supine diastolic blood pressure was significant greater for patients treated with NIF GITS than for patients treated with NIF CC (NIF GITS patients, -12.0 mm Hg; NIF CC patients, -8.4 mm Hg; P < 0.001). Because the upper bound of the confidence interval was >3 mm Hg, equivalence cannot be claimed. No statistically significant differences were noted for the comparison of mean 24-hour ambulatory blood pressure monitoring changes. Both formulations were well tolerated. © 1995.