The technique described in the preceding paper was applied to 12 abnormal sera selected for their increase in one or more B12-binding proteins. Even in the presence of large amounts of R-type binder, the ammonium sulfate technique gave a reliable separation of R binding proteins from TC II. Measurement of the TC II in abnormal sera gave results identical to those obtained by the more standard gel filtration. The R binders of four subjects with myeloproliferative disease were further separated into alpha2-R and alpha1-R. The pattern of B12 binding of polycythemia vera (PV) was an exaggeration of the normal pattern. Binding to alpha2-R was three to four times that to alpha1-R, although the total amounts bound to both were increased. In chronic myelogenous leukemia (CML), both alpha2-R and alpha1-R were also increased, but in contrast to binding in normal sera, alpha1-R predominated. In order to interpret the findings, either whole serum R or alpha1-R and alpha2-R from patients with myeloproliferative disease were subject to isoelectric focusing. Alpha2-R consisted pricipally of components isoelectric at pH 2.9, 3.0, and 3.1. These components were present in only minor amounts in normal serum and were somewhat increased in the serum of PV. These components were very much increased in the serum of CML and predominated. Alpha2-R consisted of those components isoelectric at pH 3.4,3.6, and 4.0. These components predominated in the unsaturated binding capacity of normal sera and that of PV. It was concluded that the division of plasma R binders into alpha1-R and alpha1-R by the technique described provided information useful in the study of myeloproliferative diseases.