Summary. The individual course of experimental acute renal failure (ARF) was investigated in 26 rabbits with respect to changes of renal function, plasma renin activity (PRA), and morphology.Although the cause of AI~F (i.e. renal ischemia) was identical in all animals the individual course was characterized by a great variability of functional disturbance, alterations of PRA, and the degree of histological impairment.However, already on the first postischemic day a significant difference of both plasma urea concentration and plasma renin activity between group A (surviving, n ~ 10) and group 13 (non-surviving animals, n = 16) could be found, a difference that increased in significance during subsequent days of observation.In contrast the morphology was quite variabel and the degree of histological impairment could not be correlated with chance of survival, renal function, and elevation of PRA, respectively.