&NA;The advent of molecular biology to receptor research has tremendously contributed to our understanding of the structure and function of central receptors. Essentially, most receptors can no longer be considered as static protein complexes. Instead, the subunit compositions are subject to regional and/or ontogenic changes implying that the genes of the respective receptor family are regulated differentially. It is our intention to delineate the implications of these new findings for neuropsychiatric research. For this purpose, it is necessary to review the presently available data on cloned receptor genes and the general principles that have led to the evolution of receptor families. We will point out the theoretically possible functional plasticity at central synapses and examine the basis for receptor heterogeneity. Both biologically inherent and exogenous factors can induce changes in the subunit composition of a receptor. We will consider conceivable implications of genetic variability of receptor proteins. Our conclusion is that neuropsychiatric research should favor methodological approaches that are capable of detecting receptor heterogeneity.