The stability of isradipine in an extemporaneously compounded oral liquid was studied. A suspension was prepared from the powder of commercially available 5-mg isradipine capsules and sufficient Simple Syrup, NF, to make a final volume of 50 mL. A control suspension was prepared from analytical-grade isradipine powder and Simple Syrup, NF. The final concentration of isradipine in both suspensions was 1 mg/mL. Three identical volumes of each suspension were stored in 2-oz amber glass prescription bottles, which were stored at 4 degrees C. Immediately after preparation and at 7, 16, 22, 28, and 35 days, samples were visually inspected and assayed in duplicate by high-performance liquid chromatography; the pH of the samples was also determined. At least 95% of the initial isradipine concentration remained throughout the study period in all samples of both suspensions. Color, odor, and pH did not change appreciably. Isradipine 1 mg/mL in an oral liquid compounded from Simple Syrup, NF, and powder from capsules was stable for at least 35 days in amber glass bottles at 4 degrees C.