To evaluate the bioavailability of exemestane (EXM) from self-micro emulsifying drug delivery systems (SMEDDS) and suspension formulations, a sensitive, specific, and rapid liquid chromatog.-mass spectrometric method was developed and validated.The analyte was extracted from plasma samples and detected by mass spectrometry (MS) with an atm. pressure pos.-ion chem. ionization (APCI) mode using a heated nebulizer interface.Progesterone (PGS) was used as the internal standardA Hychrome RPB-L428 column was used to perform the chromatog. separation, the mobile phase being methanol and 15 mM ammonium formate (80:20).The MS detection used a heated nebulizer interface, with multiple reaction monitoring (MRM) operated in pos.-ion mode.Both, EXM and PGS were well-separated and identified by their relative retention times, i.e., 1.13 and 1.84 min, resp.After oral administration of EXM loaded SMEDDS and suspension formulation to rats, a significant difference was observed in the pharmacokinetic behavior of drug in both the formulations, and a 2.9-fold increase in the relative bioavailability of EXM was observed with the SMEDDS as compared with suspension formulation.The developed method was found to be suitable for bioanal. of exemestane and, hence, successfully depicted the bioavailability enhancement of exemestane SMEDDS in Wistar rats.