Bis(2-ethylhexyl) phthalate is extracted from artificial kidneys, both in vivo and in vitro. Perfusion of whole blood through arterial-,venous tubing (that supplied with the dialyzer) for 1 h in vitro yielded 3.23 mg of the compound, while similar perfusion of the tubing plus the artificial kidney yielded 6.10 mg. Its mean concentration after dialysis in patients undergoing hemodialysis was 751 microgram/liter of serum. Patients who had undergone more than 50 hemodialysis treatments showed significantly higher postdialysis concentrations than patients who had undergone fewer. Uptake of bis(2-ethylhexyl) phthalate by the blood during a dialysis session followed two patterns. One set of patients showed a maximum concentration at 3 h, the second set showed a steady increase until the end of dialysis. Bis(2-ethylhexyl) phthalate appeared to be rapidly cleared from blood, most being removed within 5 to 7 h of completion of dialysis.