The MICs of ofloxacin, sparfloxacin, clarithromycin, azithromycin, and fusidic acid for clinical isolates of Mycobacterium kansasii were determined by the radiometric (BACTEC) method. All drugs except azithromycin elicited MICs for 90% of the strains tested that were lower than previously reported achievable maximum concentrations in serum. Ofloxacin, sparfloxacin, and clarithromycin had the largest maximum concentration in serum/MIC for 90% of strains ratio of the drugs tested.