The electron probe microanalyzer was used to determine the chemical compositions of the many phases that exist in the plutonium-lead binary alloy system. Probe analysis helped to identify these phases as having the following stoichiometries: Pu3Pb, Pu5Pb3, Pu5Pb4, Pu4Pb5, PuPb2, and PuPb3. The applicability of the Ziebold-Ogilvie empirical method (described in this report) for quantitative analysis of this system was established and its applicability to similar systems for which no standards are available is also shown. © 1969.