The resistance to betalactam antibiotics in a total of 177 clinical isolates of Haemophilus influenzae, mostly from respiratory tract samples and characterized by their betalactamase production, was studied using the cephalosporin chromogenic assay and by detecting bla(TEM) and bla(ROB) genes. A substantial number of clinical isolates carrying the bla(TEM) gene, which presented a mutation consisting of the absence of a fragment of 136 base pairs, located upstream from the coding region including the 35 but not the 10 region of the promoter were found. This suggests that a new bla(TEM) promoter exists in these strains. This finding was associated with increased resistance to the antibiotics cefaclor and loracarbef compared with normal isolates. It was also found that 3.9% of the isolates carried the bla(ROB-1) gene.