The adequate use of antimicrobial agents depends to a great degree on the results obtained from the continuous surveillance of bacterial resistance patterns. In order to determine these resistance patterns of bacterial pathogens responsible for community and nosocomial infections a sentinel surveillance program was started in 1988. An analysis of both pediatric and adult cases revealed 4942 bacteria isolated from different sites. Most samples from community infections were obtained from out patients seen in the infections disease clinic of the Hospital Civil de Guadalajara. Of the bacteria identified, 3584 were derived from community infections. Of those 1138 were gram positive and 2446 were gram-negative. The study also included 1350 nosocomial isolated of which 509 were gram-positive bacteria and 849 were gram-negative bacteria. Overall the gram-negative bacteria were more frequently Beta-lactamase producers than the gram-positive bacteria. Resistance to beta-lactam antibiotics ranged from 64-100% in gram negative bacteria and from 81.96% in some gram positive bacteria. During the last 2 years the resistance to third generation cephalosporins, imipenem and quinolones in gram-negative bacteria has steadily increased. Only through the continuous surveillance of bacterial resistance and the implementation of programs to combat bacterial resistance will the use of valuable antibiotics be prolonged and the activity of other ones be preserved for future use.