Rabbit sera collected from different blood vessels, e.g. vena renales, vena mesenterica, vena portae, vena hepatica and aorta, were electrophoresed in an urea-containing polyacrylamide gel. The albumin fraction was separated into 5-6 sub-bands. The profile of these sub-bands (electrophoretic pattern) of the sample from one blood vessel differed from that of another blood vessel. Especially, the electrophoretic pattern of serum collected from the renal vein 2h after deprivation of food differed from that of other blood vessels. Free fatty acid concentrations of each sample were also measured, and differences in these levels were observed in sera collected from different blood vessels. However, the fatty acid concentrations in serum from the renal vein were not low enough to permit detection of any abnormality in electrophoretic pattern in the albumin. This suggests the possibility of decreased concentration of lysolecithin in the renal vein which binds to albumin and changes the electrophoretic mobility of albumin, as do the free fatty acids.