['The biocompatibility of hemodialysis membranes has a substantial impact on the mortality of patients with end-stage renal failure. In the present study, the effects of hemodialysis on the intracellular amount of diadenosine pentaphosphate (Ap(5)A), a hydrophilic, anionic substance with a low molecular weight, was investigated.', 'The intracellular Ap(5)A concentrations were measured before and after hemodialysis using either polyacrylonitrile (AN69; n = 10) or polysulfone (n = 23) membranes. Ap(5)A was isolated from platelets using affinity chromatography and reversed-phase chromatography methods.', 'The Ap(5)A concentrations were quantified by ultraviolet absorption at 254 nm. The Ap(5)A concentrations were significantly higher in platelets from the patients with end-stage renal failure as compared with the 21 healthy control subjects (136 +/- 50 vs. 9 +/- 6 fg/platelet; mean +/- SEM, p < 0.01). Before hemodialysis, the intracellular Ap(5)A concentrations in platelets from 10 patients with end-stage renal failure using an AN69 membrane were not significantly different from those in platelets from 23 patients using a polysulfone membrane (93 +/- 39 vs. 155 +/- 70 fg/platelet). However, after a hemodialysis session, the intracellular Ap(5)A concentrations in platelets from patients with end-stage renal failure using an AN69 membrane were significantly lower as compared with those in platelets before hemodialysis (51 +/- 18 vs. 93 +/- 39 fg/platelet, p < 0.05) as well as compared with those in platelets from patients using a polysulfone membrane (51 +/- 18 vs. 250 +/- 59 fg/platelet, p < 0.05).'] Does the AN69 hemofiltration membrane have a decreasing effect on the intracellular diadenosine pentaphosphate concentration of platelets?