Brain serotonin 5-HT(1A) and 5-HT(2A) receptors have been implicated in both normal and pathological behavior, and in the action of anxiolytic and antidepressant drugs. In this study, detailed description and verification of a new RT-PCR technique to quantify the number of copies of 5-HT(1A) and 5-HT(2A) receptor mRNAs in the brain is presented. The number of copies of beta-actin and 5-HT(1A) or 5-HT(2A) receptor mRNAs in rat brain samples was evaluated with respect to the genomic DNA solution as the external exogenous standard. The expression of 5-HT receptors was calculated as the number of receptor mRNA copies per 100 copies of corresponding beta-actin mRNA. This presented technique is reliable, simple and can be easily set up in any neurobiological laboratory.