Lyme disease, the multisystem illness caused by the tick-borne spirochaete, Borrelia burgdorferi, has emerged as a threat to public health worldwide. It is a particularly vexing problem in the United States where it is growing in range and intensity. In fact, in some hyperendemic regions of New York and New England, Lyme disease is now such a threat that it interferes with all sorts of outdoor activities, and has even led to depreciation of real estate values. Family dogs in these areas seem to have been particularly hard hit by a near epidemic of lameness caused by Lyme arthritis. Persons at high risk for infection, such as outdoor workers, campers and hikers, suburbanites with lawns to cut, and pregnant women exposed to potentially infected Ixodes ticks, are clamouring for some means of protection beyond simple behaviour modification and tick avoidance which are known not always to work. Hence, the interest in human and veterinary vaccines against Lyme disease is growing.