The patient had received 50 to 90 tablets of 20 milligrams (mg) of baclofen from his caretaker; his normal dose had been 80 mg. He was in a coma about 12 hours and was then hospitalized. He died 5 days after admission from medical complications secondary to an overdose of baclofen. Baclofen was identified in his urine by gas chromatography/mass spectrometry. After derivatization with trinitrobenzene sulfonic acid, the baclofen was quantitated in serum and urine by high performance liquid chromatography. The concentration of baclofen in serum and urine was 17 and 760 mg/liter, respectively. Although the second reported baclofen overdose fatality, this seems to be the first reported baclofen related fatality that included quantitation of the drug in biological fluids. 4 figures and 13 references (Author abstract modified)