This study aimed to evaluate the frequency of nosocomial enterobacterial b-lactamase producing extended spectrum in patients confined in the Hospital Universitario “Antonio Patricio de Alcalá, Cumana, Venezuela, during the period September-November 2005. The production of b-lactamases and extended spectrum in vitro antimicrobial susceptibility were determined by the method of double-disk synergy and disk diffusion. It took 35 bacterial isolates and the increased number of nosocomial infections occurred in the intensive care unit and neonatology with 13/35 (37.15%) and 9 / 35 (25.72%) cases respectively. 51.42% of positive cultures occurred in samples of secretions. Klebsiella pneumoniae showed a frequency of 20/35 (57.14%). Only 27/35 isolates (77.14%) produced β-lactamases and extended spectrum Klebsiella pneumoniae was the most common species in the production of these, with 14/35 (40.0%). Enterobacteriaceae expressed greater percentage of resistance to ceftazidime (77.77%), cefotaxime (70.37%) and cefepime (40.74%). K. pneumoniae and E. coli, showed 59.25% resistance to amoxicillin / clavulanate. All showed 100% sensitivity to carbapenems.Long periods of hospitalization are major risk factors for acquiring nosocomial infections and the emergence of strains producing b-lactamases extended spectrum result from misuse of broad-spectrum cephalosporins, which poses significant challenges for the need to use carbapenems with the risk of exerting a selective pressure which in time will cause future resistance.