A candidate Lyme vaccine was administered to 20 adult volunteers following a 0, 1, 2 months vaccination schedule, with a booster at 12 months. An immune response, assessed as 'LA-2 equivalent' antibody titres using an inhibition ELISA, was induced in all vaccinees which persisted until the booster. Titres were increased 25-fold following the booster and persisted through month 24. There was a good correlation between 'LA-2 equivalent' antibody titres and a bactericidal assay (r2 = 0.86). Local symptoms were mild, resolving spontaneously within 72 h, with no reports of rash, arthralgia or other systemic symptoms. This Lyme vaccine was safe, well-tolerated and elicited an antibody response in all volunteers which persisted at least 12 months after the booster.