Ricinine (3-cyano-4-methoxy-N-methyl-2-pyridone) is a urinary biomarker that can be measured to confirm human exposure to castor bean products such as ricin. Because many consumer products contain castor oil, another castor bean product, ricinine may be detectable in the general population. The following study characterized urinary ricinine concentrations from 989 individuals who were presumed to be unexposed to ricin. An automated diagnostic method was utilized to simplify the analysis of this large sample set. Sample preparation included a 96-well polystyrene divinylbenzene high throughput extraction and preconcentration step. Purified samples were analyzed by an efficient dual column, reversed-phase liquid chromatography separation and (13)C-isotope dilution tandem mass spectrometry. In this convenience sample set, only 1.2% of the urine specimens had detectable amounts of ricinine, randomly distributed between 0.186 and 4.15 ng/mL.