The susceptibiltiy of Haemophilus influenzae to ampicillin and chloramphenicol has been evaluated during 1981, 1983 and 1985, and the production of beta-lactamase (BL) and chloramphenicol-acetyltransferase (CAT) was analysed. An increasing percentage of resistance strains was found during these years to Ampicillin and chloramphenicol, with a 37% and 25% for 1985 respectively. The combined resistance ampicillin-chloramphenicol has also increased with a 20.3% for 1985. We found a highly sigificant relation between production of BL and CAT, leaving to the conclusion that chloramphenicol is not the alternative antibiotic in case of production of BL. As a consequence of these results, in the case of meningitis for H. influenzae diagnosed in our hospitals, the empiric treatment of choice would be a third generation cephalosporin.