||Plasma concentrations of isoniazid, rifampicin, and pyrazinamide were measured in 22 diabetic and 22 non-diabetic pulmonary tuberculosis patients by high performance liquid chromatographic methods. From every patient, five blood samples were taken at 0.5, 1, 2, 3, and 4 hours after witnessed ingestion of antituberculosis agents. The maximum plasma concentration (Cmax) and the time to reach the Cmax (Tmax) for each drug were determined directly from the concentration-time profile. Area under the curve (AUC) was calculated from isoniazid and rifampicin only. The presence of diabetes mellitus did not significantly affect any pharmacokinetic parameters of the three agents. AUC0-24h of isoniazid was significantly higher in female patients. The AUC0-24h of rifampicin was significantly correlated with patients’ age. Weight-adjusted dose of each drug positively and significantly correlated with the corresponding drug Cmax.