The goal of this study is to improve understanding and management of postinfectious chronic fatigue. The first specific aim is to determine whether post Lyme syndrome (PLS) is antibiotic-responsive. The second is to determine whether cerebrospinal fluid (CSF) markers in these patients predict treatment response. The third aim is to determine whether premorbid psychosocial factors predict poor treatment outcome. Post treatment Lyme syndrome patients (N=50) will be evaluated at entry for fatigue, CSF and cognitive disturbances. Patients will be randomized to receive four weeks of intravenous ceftriaxone or placebo treatment. Patients will be re-evaluated at one month post treatment for fatigue response, and at six months post treatment for fatigue, CSF and cognitive response.