Demonstration of BDV-specific serum antibodies, the isolation of BDV from cerebrospinal fluid of neuropsychiatric patients, and the recent demonstration of BDV antigen and BDV-RNA in human brain tissues strongly suggest that BDV can infect humans. Isolation of BD virus from brain tissue is needed for final proof. There is still great controversy about the question of whether BDV antigen, BDV-RNA or BDV can be detected in peripheral blood monocytes or not. Overall, the question of pathogenicity of BDV infection for humans is wide open. Investigations of human cerebrospinal fluid indicate that BDV might cause human lymphocytic meningoencephalitis and so-called symptomatic psychoses in rare cases. Seroepidemiological studies suggest a widely non-specific but possibly pathogenic role of BDV in a spectrum of psychiatric disorders.