In 1986, 1711 nymphal and adult Ixodes ricinus orginating from Berlin (West) forests were examined individually or in pools of up to 10 ticks for the presence of Borrelia burgdorferi, the etiologic agent of
Lyme borreliosis. Detection of borreliae was carried out by means of a culture method using modified Barbour-Stoenner-Kelly-Medium (BSK II). Tick populations from 14 out of 15 locations contained positive specimens. The calculated minimal infection rate of pooled ticks was 2.5% in nymphs (n = 1365), 10.2% in females (n = 59), and 5.3% in males (n = 114). Among those ticks examined individually, none of the nymphs (n = 49) proved to be positive but B. burgdorferi was isolated from 8.2% of the females (n = 73) and 7.8% of the males (n = 51). Fifty-five out of 56 isolates were identified as B. burgdorferi by means of an indirect immunofluorescence test (IFT) using monoclonal antibody H 5332. From these results B. burgdorferi must be considered as being present in the Berlin area.