Regulatory measures and public concerns regarding bisphenol A (BPA) have led to its replacement by structural analogs, such as Bisphenol S (BPS), in consumer products. At present, no toxicokinetic investigations have been conducted to assess the factors determining human internal exposure to BPS for subsequent risk assessment. Toxicokinetic studies require reliable analytical methods to measure the plasma concentrations of BPS and its main conjugated metabolite, BPS - glucuronide (BPS - G). An efficient on - li ne SPE - UPLC - MS/MS method for the simultaneous quantification of BPS and BPS - G in ovine plasma was therefore developed and validated in accordance with the European Medicine s Agency guidelines for bioanalytical method validation. This method has a limit of quantification of 3 ng mL - 1 for BPS and 10 ng mL - 1 for BPS - G , a n analytical capacity of 200 samples per day, and is particularly well suited to toxicokinetic studies. Use of this method in toxicokinetic studies in sheep showed that BPS, like BPA, is efficiently metabolized into its glucuronide form . However, the clearance s and distribution s of BPS and BPS - G were lower than those of the corresponding unconjugated and glucuroconjugated forms of BPA .