Multilocus enzyme analysis by polyacrylamide gel electrophoresis (PAGE) was used to analyse 335 isolates of S. typhi from several provinces where high morbidity of typhoid fever was observed in recent years. We analysed 7 metabolic enzymes encoded by chromosome. The results showed that all the enzyme loci were polymorphic. The average alleles per locus was 7.4 (2-19): the mean genetic diversity per locus was 0.498 (0.198 0.883). There were 147 distinctive electrophoretic types (ETs) in 335 isolates. With cluster analysis by the average-linkage method, we found that there were 22 subclones, 12 clones among all isolates studied. Most isolates in 1988 from both Jiangsu and Zhejiang provinces belonged to one clone; the isolates from Guangxi Province in 1990 and parts of Hubei isolates belonged to one clone; the isolates from Hunan and Guizhou provinces during several-year period were homogeneous. However, the isolates from Xinjiang Autonomous Region were remarkebly different from other provinces, belonging to a particular clone. We also observed that the isolates from an outbreak or epidemic were from a one subclone.