We examined the activation of complement in cultures of embryonic rat hippocampal neurons exposed to patients' CSF and determined whether there is complement deposition in tumors (21 ovarian teratomas, 1 pancreatic, 1 testicular and 1 breast tumor) and brain (2 biopsies and 3 autopsies) of patients with anti-NMDAR encephalitis, and in the hippocampus of rats previously infused with patients' antibodies for 2 weeks.