The serum and cerebrospinal fluid (CSF) pathology of patients with sudden sensorineural hearing loss (SHL), both seropositive and seronegative to Borrelia burgdorferi (Bb), was prospectively studied. Nineteen consecutive patients were included and trends between the degree of hearing recovery and serum/CSF pathology and given therapy were examined. The pilot study showed a high prevalence (68%) of pathology in serum and CSF in patients with SHL. In 54% of the patients, elevated levels of CSF proteins and/or pathological CSF cell counts were present without positive antibodies to Bb. Positive levels of antibodies against Bb or pathological proteins in CSF were associated with better hearing recovery (means of 47.2 and 51.7%, respectively). The audiometric configuration "high frequency sloping" hearing impairment was associated with the lowest degree of hearing recovery. Patients with SHL and positive serology to Bb who received antibiotic treatment (oral tetracycline), with or without steroids, had the best hearing recovery in this study (61.7 and 48.4%, respectively). In conclusion, we found a high prevalence of serum and CSF pathology in a consecutive group of patients with SHL. Early appropriate antibiotic treatment may prevent the development of major late complications of Lyme disease/borreliosis. We also find it justified to perform more general serological analyses, including CSF analysis, in patients with SHL. A more liberal approach to testing and development of test protocols for SHL patients will increase our knowledge in this field.