We evaluated saliva concentration as a parameter of therapeutic drug monitoring (TDM) of Ofloxacin (OFLX) in patients with severe renal failure (CRF). Saliva OFLX concentration correlated closely with serum OFLX concentration as shown in healthy subjects, although it was significantly lower (about three-quarters), indicating that OFLX had less penetration into saliva in patients with renal failure. Saliva concentration was almost equal to serum concentration during hemodialysis, which might have been due to the constant dialysis of OFLX. In conclusion, saliva concentration was useful for TDM of OFLX in patients with CRF, as it is in healthy subjects.