For the enhancement of sample loadability and concentration sensitivity in capillary zone electrophoresis/mass spectrometry (CZE/MS) on-line isotachophoresis/capillary zone electrophoresis (ITP/CZE) in a single capillary prior to mass spectrometric detection is described for clenbuterol and some analogues. Concentration detection limits were found to be in the nanogram per millilitre range. The applicability of ITP/CZE/MS as a trace analysis technique is demonstrated by the determination of some beta-agonists in calf urine.