A simple and rapid method for analysis of free and conjugated cresols in biological fluids was developed. Prior to and following freeing of the conjugated cresols by acid hydrolysis in a sealed ampoule, free cresols were extracted by Extrelut column extraction, determined by gas chromatography, and confirmed by gas chromatography-mass spectrometry. In a non-fatal case of cresol intoxication a 46-year-old male had ingested about 100 ml of a saponated cresol soap solution. The concentrations of xylenol (2,4- and/or 2,5-dimethylphenol) and p- and m-cresol in the serum sample collected on admission were 15.8 micrograms/g, 43.3 micrograms/g and 73.8 micrograms/g, respectively. The total cresol concentration of 117 micrograms/g in the serum is within the range of fatal concentrations, and it is suspected therefore that the patient's recovery was due to adequate therapy alone.