A method using gas chromatography with organic nitrogen-sensitive detection is described for measurement of antipyrine and aminopyrine concentrations in biological fluids. The analysis was performed isothermally on 3% SP-2250 DB after alkalinized saliva was extracted into chloroform. Phenacetin served as internal standard. Low oral doses of antipyrine (1.0-1.8 mg/kg) and/or aminopyrine (2 mg/kg) were measured accurately in saliva of normal human subjects. The standard curves for antipyrine and aminopyrine were linear from 0 to 10 microgram/ml. The coefficient of variation, determined at a salivary concentration of 2 microgram/ml, was 1.7% for antipyrine and 2.4% for aminopyrine. Saliva concentrations obtained by this method in normal human subjects after either an oral dose of antipyrine (18 mg/kg) or aminopyrine (9 mg/kg) agreed closely with those determined by the flame ionization gas-chromatographic method used to measure higher concentrations of antipyrine and aminopyrine. Antipyrine (1.8 mg/kg) administered concomitantly with aminopyrine (1 mg/kg or 2 mg/kg) to normal male volunteers prolonged mean saliva antipyrine half-life by about 25-33% compared to values obtained when these same subjects received the same dose of antipyrine alone.