Five previously unmapped proteins (5a, 7d, 8, 9b, and 10) were located on the proteolytic processing map of the polyprotein. One of the proteins, 9b, appears to be the sister fragment of a cleavage reaction (P3-9 leads to P3-9b + VPg). Two of the other newly mapped proteins, 8 and 10, have been identified as sister fragments of X-related proteins 3b and 5b; thus, P2-3b leads to P2-8 + P2-5b and P2-5b leads to P2-10 + P2-X. The remaining proteins, 5a and 7d, mapped in the 1b protein and appear to result from the cleavages P3-1b leads to P3-5a + P3-6b and P3-4b leads to P3-7d + P3-6b. These assignments account for over 95% of the total polioviral proteins and complete the mapping of the major processing pathways.