In solid form, amphotericin B and amphotericin B methyl ester free base exhibit similar stability. Acid salts of the methyl ester derivative stored under identical conditions are less stable. In solution, amphotericin B is generally more stable than its methyl ester salts. However, when pH is adjusted to 6.0 and storage temperature held at 5°C the methyl ester salts reflect the stability exhibited by the parent compound, amphotericin B.