Because of the ability of 8-hydroxyquinoline sulfate (8-HQS) to irreversibly bind metals from rubber stoppers, the stability of 8-HQS in tuberculin solutions was investigated. For the determination of 8-HQS, a simple and sensitive reversed-phase HPLC method with detection at 240 nm was developed and validated. Rapid decreases in concentrations of 8-HQS were found in samples stored in original vials which were exposed to different temperatures and vial positions.