From 1991 to 1995 potential tick vectors of Lyme disease were studied in the forests and pastures in Gansu province. The ticks were collected from different species of wild animals and livestock. After identification, some specimens of each tick species were dissected for detecting the spirochete Borrelia burgdorferi under a dark-field microscope. Other specimens were cultured and identified with monoclonal and polyclonal antibodies. The morphology of the organisms was observed with an electron microscope. From two endemic areas of Lyme disease in Gansu province, 16 species of ticks belonging to 7 genera of 2 families were identified. The overall B. burgdorferi infection rate detected from midgut smears of the four infected tick species was 12.16% (22/181). The infection rates of each species were as follows: Dermacentor silvarum 13.33%, D. nuttalli 12.68%, Haemaphysalis japonica 20.0%, Ixodes crenulatus 3.57 %. Sixty-five pools of D. silvarum and D. nuttalli and H. japonica were inoculated and cultured in BAS-II media; the positive rate for B. burgdorferi was 7.32% (3/41) for D. silvarum, 36.84% (7/19) for D. nuttalli and 40% (2/5) for H. japonica.