The use of non-heartbeating (NHB) donor kidneys has led to the search for new methods of viability-testing. We investigated, in a canine model, the relationship between the filtration of dextran 12, 000 into urine and a certain period of warm ischemic time (WIT) during machine perfusion. Twenty-four canine kidneys were divided into three groups, sustaining 0 min, 30 min or 60 min of WIT. After cooling and flushing, the kidneys were perfused on a perfusion machine for 8 h. Three hundred milligrams of dextran 12,000 was added to the perfusate. In the perfusate, dextran and lactate dehydrogenase (LDH) concentrations were measured. Dextran concentrations were also analysed in urine. Intrarenal vascular resistance (IRR) was calculated from pressure and flow characteristics. The 30WIT group showed a higher dextran excretion rate than the other two groups. IRR and LDH measurements showed lower levels in the ischemic groups compared with the control group. Dextran 12,000 is not suitable as a viability test but does show interesting results regarding the low LDH and IRR levels in the ischemic groups.