Objective: To determine the pharmacokinetics of pergolide after IV administration to horses. Animals: 8 healthy adult horses. Procedures: Pergolide mesylate was administered IV at a dose of 20 Âµg/kg (equivalent to 15.2 Âµg of pergolide/kg) to each horse, and blood samples were collected over 48 hours. Pergolide concentrations in plasma were determined by means of high-performance liquid chromatography'tandem mass spectrometry, and pharmacokinetic parameters were determined on the basis of noncompartmental methods. Results: After IV administration of pergolide, mean ± SD clearance, elimination halflife, and initial volume of distribution were 959 ± 492 mL/h/kg, 5.64 ± 2.36 hours, and 0.79 ± 0.32 L/kg, respectively. Conclusions and clinical relevance: With an elimination half-life of approximately 6 hours, twice-daily dosing may be more appropriate than once-daily dosing to reduce peak-trough fluctuation in pergolide concentrations. Further pharmacodynamic and pharmacokinetic studies of pergolide and its metabolites will be necessary to determine plasma concentrations that correlate with clinical effectiveness to determine the therapeutic range for the treatment of pituitary pars intermedia dysfunction.