A method for determining susceptibility of Mycobacterium tuberculosis to one or more antibacterial drugs proposed for therapy of a tuberculosis patient, said method comprising the following steps: A) subjecting a clinical isolate from said patient to conventional preliminary procedures for decontamination of said clinical isolate and incubation of the resulting M. tuberculosis in liquid culture medium until a visible growth is observed; B) adding to a first portion of liquid culture resulting from the previous step a selected antibacterial drug while keeping a corresponding second portion of liquid culture as a control, incubating at 37°C for a selected time and then collecting the M. tuberculosis cells from the respective cultures, and lysing said cells; this operation being repeated for each antibacterial drug proposed for therapy of said patient; C) adding to the respective portions of cell lysates obtained from the previous step a spin probe selected from the group consisting of: 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine, 1-hydroxy-4-methoxy-2,2,6,6-tetramethylpiperidine, 1-hydroxy-3-methoxycar-bonyl-2,2,5,5-tetramethylpyrrolidine and other spin probes used for detection of ROS in EPR (electron paramagnetic resonance) techniques; acquiring EPR spectra from each respective portion of cell lysates obtained upon addition of said spin probes at fixed time intervals starting from 1-5 minutes after the respective addition, for a total time of from 10 to 60 minutes, measuring the intensity of the first peak of the respective spectrum at each time interval to obtain the growth rate of said intensity in time and comparing said growth rate with the growth rate obtained for the corresponding control; wherein a growth rate substantially higher than in the corresponding control is an indication of susceptibility of the M. tuberculosis present in the clinical isolate to the antibacterial drug tested, while a low growth rate, substantially equal to the growth rate in the corresponding control is an indication of resistance of said M. tuberculosis to the antibacterial drug tested. A) subjecting a clinical isolate from said patient to conventional preliminary procedures for decontamination of said clinical isolate and incubation of the resulting M. tuberculosis in liquid culture medium until a visible growth is observed; B) adding to a first portion of liquid culture resulting from the previous step a selected antibacterial drug while keeping a corresponding second portion of liquid culture as a control, incubating at 37°C for a selected time and then collecting the M. tuberculosis cells from the respective cultures, and lysing said cells; this operation being repeated for each antibacterial drug proposed for therapy of said patient; C) adding to the respective portions of cell lysates obtained from the previous step a spin probe selected from the group consisting of: 1-hydroxy-3-carboxy-2,2,5,5-tetramethylpyrrolidine, 1-hydroxy-4-methoxy-2,2,6,6-tetramethylpiperidine, 1-hydroxy-3-methoxycar-bonyl-2,2,5,5-tetramethylpyrrolidine and other spin probes used for detection of ROS in EPR (electron paramagnetic resonance) techniques; acquiring EPR spectra from each respective portion of cell lysates obtained upon addition of said spin probes at fixed time intervals starting from 1-5 minutes after the respective addition, for a total time of from 10 to 60 minutes, measuring the intensity of the first peak of the respective spectrum at each time interval to obtain the growth rate of said intensity in time and comparing said growth rate with the growth rate obtained for the corresponding control;