This paper is to report the development of a rapid and sensitive method for the determination of s-oleylpropanolamide (OPA) in various tissues of rat (brain, heart, lung, liver, spleen, small intestine, kidney, adipose tissue and muscle), and to assess the applicability of the assay to tissue distribution. OPA was extracted by liquid-liquid extraction method with undecylenoylethanolamide as an internal standard. The concentrations of OPA were determined by LC-MS/MS after a single intragastric dose of 50 mg x kg(-1) at 4 time points (5 rats per group). With multiple reactions monitoring mode (MRM) the limit of quantification (LLOQ) was determined at 1 microg x L(-1). The calibration curve was linear from 1 to 2 x 104 microg x L(-1) (r > or = 0.999 0) for tissue homogenates. Validation parameters such as accuracy, precision and recovery were found to be within the acceptance criteria of the assay validation guidelines. The highest concentration was found in small intestine (the highest time point is 15 min) and heart (the highest time point is 90 min). The assay is rapid, sensitive and applicable to studying tissue distribution of OPA in rats.