Colloidal solutions are used with increasing frequency as plasma replacement, in addition to thrombosis prophylaxis, for treating disturbances of the microcirculation and hemodilution as well as for cases of decreases in blood pressure during hemodialysis and hemofiltration treatments. The effects of the dextran, hydroxyethyl amylum and gelatine preparations available very greatly, for example with regard to expander effect, half life, elimination etc. Gelatine solutions have a particularly short intravascular retention and therefore appeared to us to be especially suitable for treating decreases in blood pressure and states of shock during hemodialysis and hemofiltration. We examined the behaviour of 5,5% oxypolygelatine (OPG) in 11 patients during dialysis treatment (6 patients with a residual diuresis smaller than 500 ml/24 h, 5 patients with a residual diuresis larger than 500 ml/24 h). Before each of the 12 treatments 250 ml OPG was administered to all patients. 48 hours later 86-93% of the infused OPG had been eliminated. Despite repeated doses no remarkable OPG cumulation was registered.