To assess the beliefs and practice habits regarding Lyme disease among practitioners, questionnaires were sent to physicians in a seven-county Lyme-endemic region. One hundred twenty-four evaluable responses were returned from 53 family physicians, 39 pediatricians, 27 internists, and five subspecialists who diagnosed three to four cases of Lyme disease per year, on average. The majority presented with erythema migrans (EM) or other early symptoms, although arthritis was the presenting sign in 16%. The enzyme-linked immunosorbent assay (ELISA) was the most frequently ordered diagnostic test, but 45% of respondents did not specify which test when ordering Lyme serology. The majority would use amoxicillin or doxycycline to treat EM in children or adults, respectively. Nearly all would use ceftriaxone for meningitis, and half would use it to treat Lyme arthritis or Bell's palsy. Physicians differed markedly in the duration of therapy they would prescribe. Eighty-three percent would treat a patient for possible Lyme disease with antibiotics (many intravenously), even in the absence of EM or positive serology. Thirty-five percent of practitioners prescribed antibiotics for deer-tick bites. Our survey documents significant variation in approaches to Lyme disease among primary-care physicians and suggests the need for well-designed clinical trials, continuing basic research, and physician education.