We investigated the levels of prolactin (PRL) and interleukin-6 (IL-6) in the cerebrospinal fluid (CSF) and serum of systemic lupus erythematosus patients with central nervous system involvement (CNS-SLE), and examined whether PRL and IL-6 have a relationship. Serum and CSF PRL and IL-6 were measured in the following groups of patients and controls: group I: seven patients with CNS-SLE; group II: three SLE patients without CNS involvement (non CNS-SLE); group III: 10 patients with neurocysticercosis; and group IV: six healthy women. The patients were clinically assessed. CSF PRL and IL-6 were elevated in group I (CNS-SLE) in comparison with all other groups (p<0.001). In addition, four of seven patients had higher levels of IL-6 and PRL in CSF than in serum. A positive correlation between PRL and IL-6 in CSF of SLE was observed (r=0.88, p<0.001). The mean serum PRL concentrations were not significantly different in all groups, but high levels of IL-6 were found in the serum of group I in comparison with groups II and IV (p<0.001). The serum levels of group III were not different from those of group I. These results demonstrate the presence of intrathecal synthesis and elevations of CSF PRL and IL-6 in active CNS-SLE involvement and indicate that measurements of CSF PRL and IL-6 may be useful in the evaluation of neuropsychiatric lupus erythematosus.