Abstract 1. Introduction of radioligand binding techniques has opened new possibilities in the study of the biological basis of psychiatric disorders. 2. The possible role of CNS receptors in schizophrenia, depression, anxiety, Huntington's disease and Alzheimer's dementia is discussed. 3. Data are presented in a systematic manner starting with the identification of receptors which appear to be the primary locus of action of drugs currently used in the treatment of these disorders. 4. A review of the data on the changes in receptor levels and/or affinity that might be associated with the respective disease follows. 5. Changes in receptor number and/or affinity after chronic drug therapy are outlined and the possible utilization of radioligand binding techniques in drug plasma level determination is discussed.