The application of reversed-phase high-performance liquid chromatography (HPLC) to the determination of isoproterenol sulphate in human plasma and urine was investigated. Sulphoconjugation of the inactive isomer of isoproterenol was chosen as an experimental model to study individual variations in the rate of sulphation of phenols in man. This approach allowed the ingestion of relatively large amounts of drug and detection of the conjugated material after acid hydrolysis, using alumina clean-up and HPLC with amperometric detection. This method was found to be rapid, sensitive, precise and suited to pharmacokinetic studies in man.