The application of high-performance liquid chromatography to resolve the individual alkaloids present in marketed Cinchona alkaloids was investigated. Normal-phase and several reversed-phase systems were evaluated. The proposed procedure uses an alkylphenyl column; it adequately resolves quinidine, quinine, dihydroquinidine, dihydroquinine, cinchonine, cinchonidine, dihydrocinchonine and dihydrocinchonidine. Epiquinidine, epiquinine, quininone and quinitoxine are also resolved from quinidine and dihydroquinidine. This high degree of resolution enables the analysis of quinidine and its salts for their usual composition and establishes the absence of any cross-contamination or decomposition. The proposed procedure was applied to currently marketed samples of quinidine salts and their dosage forms. It was also applied to samples that were cross-contaminated or which contained decomposition products.