The effective and well tolerated dose of isradipine was determined in 130 Filipino patients with mild to moderate essential hypertension in a multicentre study with a 2-week placebo pretreatment period followed by an 8-week active treatment period. 37 male and 93 female patients (mean age 51 years, mean weight 59.9kg) participated in the study. Average systolic/diastolic blood pressure on admission was 163.8/103.7mm Hg. Results showed isradipine normalised sitting diastolic blood pressures in 109 of 130 (83.8%) patients. 71 patients (54.6%) were receiving isradipine 1.25mg twice daily while 38 patients (29.2%) required a dose of 2.5mg twice daily. A drop of greater than or equal to 10mm Hg in sitting diastolic blood pressure was achieved in 71 patients (54.6%) administered isradipine 1.25mg twice daily and 44 patients (33.8%) on isradipine 2.5mg twice daily. Heart rate was not significantly changed with either dosage. Drug-related adverse effects were only transient in duration and mild to moderate in severity. No patient discontinued treatment because of these effects. This study provides confirmatory evidence of the clinical efficacy and tolerability of a daily dose of less than or equal to 5mg isradipine in Filipino patients with mild to moderate hypertension.