The disposition of piperacillin given as a 4 gm i.v. infusion was assessed during an interdialytic period and during hemodialysis in 12 chronic hemodialysis patients. Piperacillin concentrations in serum and dialysate were determined by HPLC. The half-life decreased from 2.84 +/- 2.04 h (mean +/- SD) during the interdialytic period to 1.30 +/- 0.43 h during the hemodialysis period (p = 0.008). Piperacillin total body clearance was 74.9 +/- 34.0 ml/min during the interdialytic period and the hemodialysis clearance was 92.4 +/- 30.0 ml/min. A significant change in the volume of distribution was observed from the interdialytic to dialytic period (0.21 +/- 0.06 vs 0.26 +/- 0.07 l/kg) (p = 0.026). A significant correlation between the hemodialysis clearance of piperacillin and hemodialysis clearance of creatinine and blood flow rate was also noted. No significant rebound in serum piperacillin concentrations was observed after cessation of hemodialysis. Approximately 46% of the amount of piperacillin in the body was removed by dialysis.