Schizophrenia and certain forms of idiopathic mental retardation may result from covert immune complex disease of the basal lamina of the choroid plexus, a process already known to cause covert transport dysfunction in similar structures of, for example, skin, bowel, kidney, and endocrines. Plexial attack could lead to cerebrospinal fluid contamination and then, via an “open” ependyma, to neurotransmitter dysfunction in the periventricular limbic brain. The immune complex mechanism implies polygenic induction, direct or autoimmune, of immune sensitivity to exogenous agents and is thus compatible with the genetic picture in schizophrenia. Candidate agents include viral coat peptides and cereal grain glutens. The glutens are known to cause immune complex skin and bowel disease variants, and some empirical evidence links them to schizophrenia. Only newer immunofluorescence methods can detect the pathology, which is otherwise silent. Systemic lupus erythematosus provides a model since it is a genetic immune complex disease strongly associated with schizophreniform psychoses, exhibits choroid plexial immunofluorescence but no central nervous system pathology by ordinary methods, and may be triggered by viruses.