From 1987 to 1997, primary vectors of borrelia burgdorferi sensu lato (B.b.s.l.) were investigated in China. A total number of 17,000 ticks collected from 20 provinces, city and autonomous region were classified, including 2 families 8 genus 23 species. There were 108 isolates of B.b.s.l. discovered from 8 species of ticks, including Ixodes persulcatus, I. granulatus, I. acutitarsus, Haemaphysalis concinna, H. longicornis, H. bispinosis, H. cornigera taiwana and Dermacentor silvarum. Ixodes persulcatus was found as the dominant species, accounted for more than 80% of the total number of collected ticks. 20 to 45 per cent adult Ixodes persulcatus contained spirochetes as determined by direct immunofluorescence in the northeast and northwest areas. Seasonal change of adult Ixodes persulcatus was coincident with patients with erythema chronicum migrans. These studies proved that Ixodes persulcatus played a leading role in the transmission of B.b.s.l. to human being in northern region of China. Haemaphysalis bispinosis and Ixodes granulatus were identified as the dominant species with 16 to 40 per cent adult Haemaphysalis bispinosis and 24% per cent adult Ixodes granulatus containing spirochetes as determined by direct immunofluorescence in the southern region of China. Haemaphysalis bispinosis and Ixodes granulatus were proved to be important vectors of B.b.s.l. in the southern area of China.