The red cell expansion in polycythemia vera (PV) causes hyperviscosity affecting blood flow, which plays a major role in the pathogenesis of both microcirculatory disturbances and ultimately thromboses. Ischemia-modified albumin (IMA) is produced during an ischemic states and is present in blood in early and easily detectable levels. This study investigated whether IMA is a useful adjunct in the determination of ischemia in patients with PV, prior to them exhibiting clinical evidence of thrombotic complications. Blood IMA levels were determined in 20 PV patients and in 20 healthy individuals using a method described by Bar-Or. Mean IMA levels in the PV group were significantly higher than those of the control group (P<0.05). At the optimum cutoff point (0.193 absorbance units), the sensitivity and specificity of IMA were 80 and 100% to ischemia, respectively. In conclusion, IMA may be a valuable biochemical marker in predicting tissue ischemia in PV before the signs of vascular disturbances occur.