A simple and rapid method was validated to determine furosemide in whole blood. The experimental work was performed so that all validation parameters are considered simultaneously in a one-day assay protocol. A solid-phase extraction procedure using BondElut-LRC Certify columns was used to extract this compound from blood samples, while ketoprofen was used as an internal standard. The extracts were analyzed by gas chromatography-electron ionization-mass spectrometry after on-column derivatization with trimethylanilinium hydroxide (0.2M in methanol). Calibration curves were prepared daily, between 0.10 and 5.00 microg/mL, and the correlation coefficients were above 0.9910. The calculated limits of detection and quantitation were 0.010 and 0.045 microg/mL, respectively. Control samples at low, medium, and high concentrations (0.30, 0.75, and 3.00 microg/mL) of furosemide of an independent source were measured in the same day. Precision and trueness, calculated in terms of relative standard deviation (%), were less than 15% for all concentration levels. The relative recoveries calculated for the three levels of the control samples were 104%, 89%, and 91%, respectively. In general, a sensitive, specific, and reliable procedure has been developed for the determination of furosemide in whole blood samples and was found suitable for the application in postmortem forensic toxicology routine analysis.