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Recently a small number of patients were observed in two psychiatric hospitals in the Netherlands with clozapine intoxications that complicate or mimic infections. These patients were on chronic medication and normally had stable clozapine blood plasma levels. This article presents four of these cases. Medline was searched for reports of similar cases. A hypothesis was formulated and tested by literature study. Immune modulatory and toxic effects of clozapine protein reactive metabolites or haptens, may play a role in the development of inflammation. Clozapine has a direct influence on different cytokines resembling an inflammatory reaction. Infection or inflammation could induce bioactivation of clozapine into its nitrenium ion that can exert a toxic reaction that induces apoptosis and gives rise to elevated cytokine levels. Clozapine can function as a hapten and induce an IgG, IgM or IgE mediated hypersensitivity reaction. The cytokines released during infection or inflammation downregulate the clozapine metabolism in the P450 system through CYP 1A2. Clozapine plasma levels should be monitored closely if an inflammatory or infectious process is suspected. [Copyright &y& Elsevier]