Clozapine is an effective antipsychotic drug for the treatment of therapy-resistant schizophrenia. Mandatory screening of white blood cells is a safety measure for the early detection of agranulocytosis caused by treatment with clozapine. However, so far, there is no standard screening for two other potentially lethal side-effects, namely diabetic ketoacidosis and gastro-intestinal hypomotility. The current situation is weighed up on the basis of a comparison of the chances that these side-effects can occur and cause death. The conclusion is that weekly or monthly screening should be carried out for all these side-effects.