Measurements of beta-endorphin-like immunoreactivity have been performed in CSF and plasma of patients with schizophrenia and other neuropsychiatric disorders. The detection limit of the RIA was between 20--50 pg/ml (6--15 fmole/ml). In CSF the quantity of beta-endorphin-like immunoreactivity ranges up to 65 pg/ml. The data from schizophrenics and other neuropsychiatric patients show no obvious deviation from the results in a control group of medical patients with normal CSF findings. In plasma the immunoreactive beta-endorphin-like material ranges up to 250 pg/ml. There is only a small tendency to higher values in schizophrenic patients, if compared with different types of neuroses and affective and organic psychoses. In a second series of experiments also this tendency could not be reproduced. In 9 electroconvulsive treatments an increase of blood beta-endorphin-like immunoreactivity was observed 7 times. A possible endorphinergic mechanism in the mode of action of electroconvulsion is hypothesized.