The genomic variability of poliovirus was examined by analyzing the restriction fragment length polymorphism of a reverse-transcribed genomic fragment amplified by the polymerase chain reaction. The fragment was a 480-nucleotide sequence of the poliovirus genome coding for the N-terminal half of the capsid protein VP1, including antigenic site 1. The identification of a pair of generic primers flanking this fragment allowed its amplification in practically all the poliovirus strains tested so far (more than 150). By using the restriction enzymes HaeIII, DdeI, and HpaII, strain-specific restriction profiles could be generated for the amplified genomic fragment of each of the six reference poliovirus strains tested: one representative wild poliovirus of each of the three serotypes (P1/Mahoney, P2/Lansing, and P3/Finland/23127/84) and the three Sabin vaccine strains. When 21 poliovirus field isolates previously identified as Sabin vaccine-related were tested, they showed restriction profiles identical to those of the originating homotypic Sabin virus, demonstrating the conservation of these profiles during virus replication in humans. These profiles could thus be used as markers for Sabin-derived genotypes. To compare the distribution of poliovirus genotypes in nature before and after the introduction of poliovirus vaccines, the restriction profiles of the amplified genomic fragment of a total of 72 strains of various geographic and temporal origins were determined. Strains isolated before the introduction of polio vaccines displayed a wide diversity of genotypes. In contrast, wild (Sabin unrelated) strains isolated after vaccine introduction, during a single epidemic in a particular geographic area, showed identical or very similar restriction profiles, indicating the circulation of predominant regional genotypes. Our results indicate that the assay we developed for the analysis of the restriction fragment length polymorphism of the poliovirus genome may be used to identify and characterize poliovirus genotypes circulating in nature.