Investigators propose a randomised double-blinded placebo-controlled trial to test the hypothesis that immunotherapy is an effective treatment of antibody-associated psychosis, either first episode of psychosis or relapse following previous remission. Immunotherapy for the trial consists of one cycle of intravenous immunoglobulin (IVIG: 2g/kg over days 1-4) followed by two infusions of 1g rituximab (at day 28-35, and then 14 days after the first infusion). The rationale for this regime is that it combines a rapid-action treatment (IVIG) to induce remission with a longer-action therapy (rituximab) to maintain remission. It is based on a protocol where elimination of circulating antibodies is the treatment goal, namely "desensitisation" of potential transplant patients who have multiple anti-HLA antibodies capable of inducing hyperacute rejection and also being tested in various trials on clinicaltrials.gov (NCT00642655, NCT01178216, and NCT01502267). Blinding is required to minimise placebo responses in a trial based on symptomatology.