Pergolide (PG) a semi-synthetic ergot alkaloid derivative used mainly for the treatment of Parkinson's disease is known to be a photosensitive drug substance. The major photodegradation products are PG sulphoxide (SX) and PG sulphone (SN), which are also the main impurities of the bulk drug substance. It is widely metabolized to more than 10 metabolites including SX and SN. In this work an improved photostability indicating ion-pair chromatography method for PG mesilate was developed. The method can be applied in the determination of PG and impurities in aqueous solutions and in tablets for routine analysis. This new method is appropriate for the quantitative determination of PG in the presence of its impurities and photodegradation products and can also be used for PG complexes with cyclodextrins (commonly used as photostabilizing agents). Furthermore it is suitable for the quantitation of its impurities and its thermal or photo-induced decomposition products. Separation was achieved on a ThermoQuest C(18) BDS column and Sodium octanosulphonate was used as ion-pairing agent. Analysis was performed at 223 nm. Validation parameters included: specificity, linearity, precision and accuracy, limit of quantitation and suitability. The method was found to be specific and linear for PG, as well as for SX and, SN impurities. The recovery was 100.83+/-0.46% for PG, 99.86+/-0.33% for SX and 99.77+/-1.84% for SN. Finally the photodegradation profile of PG mesilate was studied in different initial sample concentration. The obtained result revealed that: PG photolysis is catalyzed by its degradation products and that decrease of initial sample concentration reduces the rate of PG photoinduced degradation.