Biological sample clean-up procedures were evaluated for the extraction of a range of /3-agonists. Once extracted the compounds were determined by immunoassay, electrochemical techniques and supercritical fluid chromatography (SFC). Clenbuterol was isolated from liver tissue using matrix solid phase dispersion (MSPD). The technique was optimised for extract clean-up and recovery by evaluation of various wash and elution solvents using radiolabelled clenbuterol. Recovery of clenbuterol was > 90 % at three levels tested (1, 2 and 5 ng/g). MSPD was then applied to the extraction of other compounds in this class like salbutamol, mabuterol, cimaterol and terbutaline in the low ng/g range. For residues which occur as conjugates, an enzyme hydrolysis procedure was used. Sample extracts were assayed by radioimmunoassay (RIA) and enzyme immunoassay (EIA). Cyclic voltammetry (CV) was used to study the electrooxidation of salbutamol, fenoterol and metaproterenol at unmodified and Nafion-modified carbon paste electrodes (CPE’s). All compounds were oxidised irreversibly at high positive potentials at the CPE. The Nafion-modified electrode allowed the accumulation of all compounds with time, resulting in an enhanced sensitivity. The application of the Nafion-modified electrode to the analysis of fenoterol in human urine and serum extracts was demonstrated at the 10'7 and 10'6 M level, respectively. In this case the more sensitive differential pulse voltammetric (DPV) mode of detection was chosen. Finally, the application of supercritical fluid extraction (SFE) for the isolation of /3-agonists was investigated. Extracts of pure standards and liver samples, dispersed on support media (Celite and C18 material), were assayed by supercritical fluid chromatography (SFC) with UV detection.