We studied the genetic diversity within specific genes among S. typhi isolates from different geographic regions using various gene probes (Southern blot hybridization) after restriction endonuclease digestion of genomic DNA. Isolates from Malaysia, Indonesia, Papua New Guinea, India, Chile and Switzerland were studied. Polymorphisms were detected among these isolates when fliC, groEL, 16S rRNA and rfbS gene probes were used to probe restricted DNA. In contrast, homogeneity in hybridization pattern was observed when an ompC gene probe was used. Further testing was performed with gene probes for the 16S-23S rRNA spacer region, viaB, invA, and the pathogenicity island gene cluster for Salmonella spp, SPI and SPII. The present study confirms the significant genetic diversity among S. typhi isolates, not only at the total genomic DNA level, but at the level of specific genes. It would be of interest to determine any correlation between genetic polymorphisms and biological properties, especially those related to virulence.