Blood specimens were collected from villagers in Khon-Kaen province, in the north-eastern region, and in Songkhla province, in the southern region of Thailand in the pre- and post-epidemic seasons of hemorrhagic fever. The hemagglutination inhibition antibody titers of the specimens were measured against dengue virus type 2, type 4, Japanese encephalitis virus and chikungunya virus. In general, Khon-Kaen villagers showed higher levels of HI antibodies against these arboviruses than Songkhla villagers and in both areas the antibody level against chikungunya virus, a group A arbovirus, was usually much lower than those against group B arboviruses. Specimens from Khon-Kaen province had such high antibody positive rates for group B arboviruses (80-100%) from an early age (3-4 years), in the pre-epidemic season, that scarcely any increase in the positive rate was observed in the post-epidemic season. The positive rate in specimens from Songkhla province was not so high in the pre-epidemic season and some increase was seen in the post-epidemic season, especially in lower age groups (3-4 to 7-9 years). The patterns of HI antibody titers in different age groups in the Khon-Kaen and Songkhla provinces were also compared. The patterns changed with increase of ages and were also different with different viruses. The patterns for chikungunya virus were quite different from those for dengue type 2, type 4 and Japanese encephalitis virus. These results suggest that people in Khon-Kaen are exposed to group B arbovirus infections more often in childhood and attain high antibody levels more rapidly than people in Songkhla.