Lyme disease is a vector-borne disease caused by the spirochetal bacteria,Borrelia burgdorferi (Bb). It is maintained in the wild in vertebrate hosts, and transferred from host to host through feeding by ticks. Lyme disease tends to be more of a problem to humans in the eastern US than in California. Differences in the tick species (Ixodes pacificus in California, versus Ixodes scapularis in the eastern US) and the timing of the tick life cycle contribute to this difference. Our research is trying to establish the both the distribution of Lyme disease in California and the biotic and abiotic factors that influence this distribution.