Oxypolygelatin (CAS 9005-91-8, OPG) and degraded gelatin (CAS 9000-70-8, DG) have attracted the interest of many investigators as promising plasma protein substitutes. This paper deals with comparative evaluation studies on OPG and DG as regards stability and some biochemical consequences following i.v. infusions in rabbits. Accelerated aging tests showed a decrease in pH of OPG from 7.3 to 7.0. The pH of DG increased from 5.2 to 5.4 during the same period of aging. In both cases, the buffer capacity increased 3.0 to 3.5 in case of OPG and from 2.5 to 3.7 in case of DG. The relative viscosity of OPG decreased from 2.18 to 1.98 as compared to 1.79 to 1.58 in case of DG. Comparative studies on both OPG and DG postinfusion in rabbits, showed significant (p < 0.001) retention OPG in blood 24 h postinfusion, at which time, DG was practically absent. The decline in rabbit plasma protein was marked and more persistent in case of compared to DG. Plasma sodium showed a significant decline (p < 0.05) in case of OPG 1 h postinfusion, while plasma potassium showed a significant decline (p < 0.05) immediately postinfusion. In case of OPG, serum calcium showed a significant decline (p < 0.001) immediately postinfusion. This effect was marked at 1 h, 5 h and 24 h postinfusion. In case of DG, no significant changes in the levels of sodium, potassium, calcium and magnesium were observed at all time intervals postinfusion of the plasma volume expander.