The use of molecular biology techniques in the study of central nervous system (CNS) functions is currently expanding at an exponential level. The possibilities offered by such methodologies is attracting an increasing number of researchers for their broad applicability and for their promise to permit the investigation of different proteins, in particular of enzymes responsible for the synthesis and catabolism of neurotransmitters, as well as of neuroreceptors, step by step, from gene to transcription to posttranscriptional processes. Nowadays, a general knowledge of such methods and of how they can be used in CNS studies is fundamental for psychiatrists, even if not directly involved in basic research. The authors will review the most common gene expression techniques which are used in biological psychiatry. They will also present the results of some studies in which the particular methodologies of mRNA expression and in situ hybridization have been applied to the investigation of some serotonin receptor subtypes in the human brain, in parallel with binding studies.