This study investigated the susceptibility of 25 Mycobacterium tuberculosis clinical isolates to tobramycin (TBM) and clarithromycin (CLM). The effect of the drugs administered together was examined for possible synergistic effect. The median minimum inhibitory concentration (MIC) for both drugs was 8 mug/ml. In 36% of the isolates, a decrease of the CLM MIC by a single or two-fold dilution was observed when a sub-inhibitory concentration of TBM was added. The results suggest that both drugs should be investigated further as potential adjuncts to the treatment of resistant tuberculosis, in particular through new drug delivery systems such as the dry powder inhaler allowing high lung deposition.