Background: The problem of multidrug resistant M, tuberculosis (MDR TB) has increased in recent years around the world. Objetive: To analyse the evolution of resistance patteras of M. tuberculosis. Methods: Cultures of M. tuberculosis isolated from patients of two terciary care hospitals of Guadalajara, México were analyzed. Susceptibility tests were earned out by the Canetti method. Results: The annual resistance percents of 262 cultures was: 1993 1994 1995 1996 Total (a=23) (a=26) (n=64) (n=149) (=262) Isomazid 74 77 53 78 71 Rifampin 43 42 41 40 41 Pyrazinamide 22 58 67 52 54 Ethambutol 65 62 47 77 53 Streptomycin 22 46 75 56 57 Ethionamide 22 27 50 49 45 Para-aminosalicyhc-acid(PAS) 30 46 41 45 43 Ciprofloxadn - 12 30 17 20 Ofloxacin - 15 30 39 34 MDR TB (isoniazid and rifampin) 43 27 31 36 31 Conclusions: The primary drugs resistance is high, the resistance to pyrazinamide, streptomycin, ethionamide and PAS has been increasing
