Recent progresses on membrane protein dynamics and their functions are discussed. Electron transfer interactions have been analyzed by measuring rotational diffusion of cytochrome P450scc and reductases in adrenocortical mitochondria. Intracellular signal transduction in adrenocortical cells has been demonstrated by measuring the hormone-induced calcium oscillations and incorporation of low density lipoprotein using video-enhanced microscopy and laser scanning confocal microscopy. These investigations contributed significantly to the understanding of molecular mechanisms of steroidogenesis in adrenal cortex. Analysis of dynamic topology is also discussed for rat liver type cytochrome P450IA1 genetically expressed in yeast microsomes.