A quantitative method for the analysis of paraquat in blood and tissue samples has been developed using liquid chromatography-electrospray ionization-mass spectrometry. Chromatographic separation was performed on an Atlantis HILIC silica column using a mobile phase of acetonitrile/250 mM ammonium formate in the gradient mode. The method was linear from 2 to 500 ng/mL, with a correlation coefficient of 0.998. The limits of detection and quantitation in blood were determined to be 0.5 and 2 ng/mL, respectively. Intraday precision was performed in one extraction by analyzing five aliquots of three controls with different concentrations in the established linear range. Interday precision was determined by analyzing one aliquot of each control over 10 extractions. The coefficients of variation were less than 10% for both intra- and interday assays. The method has been successfully applied to blood and tissues samples from nine cases and can be used to detect the presence of paraquat in forensic testing.