Linezolid (LZD) is thought not to require dose adjustment in patients with renal dysfunction, making it a drug of choice for these patients. However, in the current study we show LZD accumulation occurring with repeated dosing during hemodialysis in a 64-year-old man receiving hemodialysis treatment. In this patient, methicillin-resistant Staphylococcus aureus (MRSA) caused an abscess under the abdominal wall due to wound infection after colon cancer surgery. Treatment was initiated with intravenous LZD (600 mg) every 12 h. However, pancytopenia and liver dysfunction occurred during the LZD administration period. A high trough level, of 15-20 microg/ml, during LZD administration was determined from stored blood biochemistry samples, and pharmacokinetic parameters, estimated by the Bayesian nonlinear least squares method, were as follows: clearance (CL), 1.56 l/h; clearance during hemodialysis (CL(HD)), 2.23 l/h; volume of distribution (Vd), 18.69 l; and area under the curve (AUC), 384.07 microg/ml . h. Simulation of the serum concentration-time profile from the estimated pharmacokinetic parameters gave a trough level about four to five times higher than that in healthy individuals in the early administration period, indicating LZD accumulation in blood. These findings suggest a causal relationship between the high LZD level and the adverse effects. The cause of the high LZD level is unclear, but the findings indicate that careful monitoring and dose adjustment of LZD is necessary in hemodialysis patients.