We report pharmacokinetic data on two gastrectomized, patients affected by tuberculosis. Drugs plasmatic concentrations were measured after seven days of oral therapy by a validated high performance liquid chromatography-mass spectrometry (HPLC-MS) method and the area under the concentration-time-curve (AUC) over 24 hours (AUC(0-24)) was calculated. A sub-therapeutic level of isoniazid was found in a patient with total gastrectomy with a C(max) of 0,395 mg\L and AUC(0-24) level of 4.75 hr*mg/L. The level of the other antitubercular drugs was adequate. These findings support the need to monitor anti tubercular drug levels to facilitate early detection of therapeutic failure, above all in patients treated with isoniazid and with potential problems on oral drugs absorption.