The stability of cyclosporine in an extemporaneously compounded paste was studied. Cyclosporine oral solution 100 mg/mL was mixed with an adhesive gel to prepare six aluminum-lined ointment tubes containing paste with cyclosporine 9.6 mg/g. Two of the tubes were stored at 37 degrees C, two at 21 degrees C, and two at 2 degrees C. Cyclosporine was extracted from samples taken on days 2, 4, 5, 7, 9, 14, 18, 22, 28, and 31, and the concentration was measured by high-performance liquid chromatography (except for samples obtained on day 2) and fluorescence polarization immunoassay. Throughout the study period, the concentration of cyclosporine remaining in the paste was > 90% of the initial concentration according to both assay methods. Cyclosporine 9.6 mg/g in a paste compounded extemporaneously from cyclosporine oral solution and an adhesive gel was stable for at least 31 days when stored in aluminum-lined ointment tubes at 37, 21, and 2 degrees C.