The subunit compositions of individual phytohemagglutinin isolectins from red kidney bean Phaseolus vulgaris were examined by isoelectric focusing and sodium dodecyl sulfate electrophoresis on polyacrylamide gels. Isoelectric focusing reveals heterogeneous but unique and non-overlapping protein band patterns for each of the homotetrameric isolectins, E4 and L4. Isoelectric focusing of the intermediate isolectins which contain both subunits (E3L1, E2L2, and E1L3) show all the protein bands common to isolectins E4 or L4 in proportions relative to their suggested subunit compositions. Polyacrylamide gel electrophoresis in a continuous sodium dodecyl sulfate buffer system gives a single protein band for all of the isolectins. In contrast, a discontinuous sodium dodecyl sulfate buffer procedure resolves isolectins E4 and L4 into single major protein bands of apparent molecular weights 31 700 (+/-600) and 29 900 (+/-200), respectively. Each of the intermediate isolectins contained both protein bands and their relative proportion, as determined by absorbance scanning, confirms the phytohemagglutinin isolectin subunit compositions as E4, E3L1, E2L2, E1L3, and L4.