Lyme disease is a tick-borne disease recently (1982-1983) shown to be caued by a spirochete. The spirochete is transmitted by ticks of the genus Ixodes. Nineteen to 61% of these ticks from endemic areas carry the spirochete. Lyme disease is a systemic illness that usually begins with a characteristic skin lesion, erythema chronicum migrans. If untreated, weeks to months later certain patients develop neurologic or cardiac abnormalities. After this, intermittent attacks of arthritis occur in some patients which may become chronic with erosion of cartilage and bone. Lyme disease is now an important public health problem with 6 to 10% of people living in some endemic areas experiencing the disease. Little is known of the host-parasite relationship nor the mechanism of pathogenesis in Lyme disease and a sensitive specific test for the serodiagnosis of this disease is needed. We plan to 1) investigate cultural conditions to improve the isolation of Lyme disease spirochetes, 2) use an experimental animal to determine in vivo antibiotic sensitivity of the Lyme disease spirochete, feasibility of a vaccine for this disease and the role of antibodies in immunity to Lyme disease, 3) study the role of human phagocytes in the host defense against the Lyme disease spirochete.