A suspension containing gelatin-castor oil microcapsules dispersed in an aqueous solution of carboxymethylcellulose was developed and tested. Its physical properties at room conditions (25° C.) are similar to those of whole blood in the mammalian body (37° C.), providing a possible tool for flow visualization under ideal conditions. In addition to having a similar density and containing deformable particles, the pseudo-blood suspension (45% by volume microcapsules) matches the pseudoplastic behavior of whole blood in the shear rate range of 20 to 100 reciprocal seconds and the Newtonian behavior of whole blood in the range of 102 to 103 reciprocal seconds. © 1969, American Chemical Society. All rights reserved.