A method is described for the determination of terbutaline and salbutamol in plasma from patients given maximal therapy for brittle asthma. The analytes were isolated by solid phase extraction on alkali-treated Bond-Elut, unmodified, silica columns and measured by high performance liquid chromatography with fluorescence detection (excitation wavelength 200 nm). The limits of detection for a 1 mL sample containing salbutamol and terbutaline were 1 microgram/L and 2.5 micrograms/L, respectively. The intra-assay precision (CV) for samples containing 25 micrograms/L was 3.6 and 5.0% respectively. This method was applied to the measurement of terbutaline in samples from patients given continuous infusions of the drug to assess whether this treatment might result in toxicity.