A recent study reporting surprisingly high beta-lactam MICs against beta-lactamase-negative ampicillin-resistant (BLNAR) strains when tested by the Etest prompted us to compare results of the Etest with those of the standard broth microdilution concerning BLNAR strains. The main concern of the current study was whether remarkably high MIC patterns of BLNAR strains in response to beta-lactam antibiotics and meropenem arise from the test method or their actual status. To confirm this, we compared results of the Etest with those of broth microdilution using 153 Haemophilus influenzae isolates with known mechanisms of beta-lactam resistance, simultaneously determining MICs by both methods and checking the mutation status of the ftsI gene. Results showed that MICs of BLNAS (beta-lactamase-negative, ampicillin susceptible) and BLPAR (beta-lactamase-positive ampicillin-resistant) strains showed consistent results by both tests with high agreement (92.59 to 100% for beta-lactams and 90 to 92.59% for meropenem). However, BLNAR and BLPACR (beta-lactamase-positive amoxicillin-clavulanate-resistant) strains showed diverse results, with agreement for beta-lactam and meropenem decreasing to 48.27% to 100% and 42.10% to 44.82%, respectively. The fluoroquinolone levofloxacin showed high agreement (98.85% to 100%) between the two methods.