It is becoming evident that the diverse electrophysiological actions of 5-HT in the central nervous system can be best formulated in terms of receptor subtypes and their respective effector mechanisms. Based on the findings described in this review, the following pattern of central 5-HT electrophysiology is emerging: 1) inhibitory effects are mediated by 5-HT1 receptors linked to the opening of K channels via pertussis-toxin sensitive G proteins: 2) facilitatory effects are mediated by 5-HT2 receptors and involve the closing of K channels, an effect which appears to be negatively modulated by activation of the PI second messenger system: 3) fast excitations are mediated by 5-HT3 receptors, most likely involving a direct interaction with an ion channel rather than through coupling with a G protein or a second messenger. Further studies will be required in a wider range of brain areas to establish the generality of these conclusions.