Pergolide, an ergot-derived dopamine D₂ receptor agonist, is used extensively as an orally administered treatment for pituitary pars intermedia dysfunction  (PPID) in horses. One of the barriers associated with pergolide determinations in plasma for pharmacokinetic applications has been the technically demanding requirement for sensitivity. The objective of our work was to develop a simple assay for the determination of pergolide in plasma and demonstrate its potential application in the study of pergolide pharmacokinetics in horses. A UPLC-MS/MS assay was developed with a simple sample preparation involving methanol protein precipitation and injection of supernatant. The assay was applied to samples from a horse dosed with10 mg pergolide (as the mesylate salt) by nasogastric intubation.  Plasma samples were collected over a 48 hour period. The assay demonstrated performance sufficient to enable application to low level pharmacokinetics studies; within-batch precision was 1.6% RSD (n=4) and accuracy -4% at the 0.14 ng/ml level, the lower limit of quantification was 0.006 ng/ml and the method detection limit 0.002 ng/ml. In the treated horse, C_max was 0.40 ng/ml and the assay easily allowed determination of plasma levels in the elimination phase to 48 hours; based on the calculated elimination rate constant, we could quantitate to 82 hours and detect drug to 103 hours post-dose. In conclusion, this assay using UPLC-MS/MS and methanol protein precipitation easily meets the challenging demands of low level pergolide analyses in plasma.