PURPOSE To evaluate the in vitro activity of fluoroquinolones against Mycobacterium abscessus and Mycobacterium chelonae isolated from outbreaks of infectious keratitis in Brazil. MATERIAL AND METHODS Micobacterial isolates were recovered from infectious keratitis cases related outbreaks that occurred in Brazil after LASIK for myopia. Two outbreaks occurred in Rio de Janeiro in 1998 and 1999, and 3 in São Paulo between 2000 and 2003. All laboratorial analysis, including molecular identification and antibiotic susceptibility testing with determination of the minimum inhibitory concentration (MIC) levels for ciprofloxacin, ofloxacin, gatifloxacin, and moxifloxacin, were performed at Universidade Federal de São Paulo in Brazil. RESULTS Fifteen samples were identified as M. chelonae, and 3 were identified as M. abscessus. The outbreaks studied were designated SP-1 in 2000; SP-2 in 2000-2001; and SP-3 in 2003, R1 in 1988 and R2 in 1999. All but 1 of the M. chelonae were resistant to all fluoroquinolones with an MIC90 greater than 32 microg/mL. The only susceptible isolate had MIC levels for ciprofloxacin, ofloxacin, gatifloxacin, and moxifloxacin of 0.38 microg/mL, 0.032 microg/mL, 0.047 microg/mL, and 0.19 microg/mL, respectively. MIC levels for all 3 M. abscessus isolates tested were greater then 32 microg/mL for all fluoroquinolones tested. CONCLUSIONS Fluoroquinolone MICs for 17 M. abscessus and M. chelonae isolates recovered from infectious keratitis cases in Brazil indicate that they are not susceptible to these drugs in vitro. Further studies to investigate the in vivo effectiveness of fluoroquinolones against mycobacteria are required because in vitro tests do not support their use in the treatment of micobacterial keratitis in this particular geographic area.