A number of diverse extracellular signals are at the cell surface specifically recognized by different types of membrane-bound receptors, which subsequently activate the relevant signalling cascades. The most plentiful group of these receptors is formed by heptahelical (or serpentine) receptors coupled to trimeric G-proteins. Trimeric G-proteins (composed of alpha and betagamma subunits) function as molecular switches that directly regulate activity of various effector molecules, such as adenylylcyclase, phospholipase C and some ionic channels. G-proteins thus play a crucial role in regulating cellular responses. Transmembrane signalling mediated by trimeric G-proteins may be seriously deranged in various pathophysiological conditions and, therefore, a great attention is currently being paid to investigation of these signalling systems. The practical significance of this research is well documented by the fact that substantial portion of medicinal drugs produced by pharmaceutical industry is oriented to amend functioning of these signalling systems. The present review is intended to provide a brief up-to-date characterization of all major components of transmembrane signaling systems regulated by G-proteins, i.e., heptahelical receptors, G-proteins and some crucial effector molecules.