The discovery of the complex regulation of mitochondria functions by hormones and signal transduction systems is one of the new and important achivements of mitochondriology. A number of hormones of all the chemical classes and with different action mechanisms stimulate many mitochondrial processes, including Krebs cycle, respiratory chain, oxidative phosphorylation, energy dependent syntheses. These effects are realized and/or reproduced by receptors, the second messengers (cAMP, Ca2+, diacylglycerol), protein and tyrosine kinases, anchor proteins, transcription factors. All the main kinases are found in mitochondria; protein kinases and/or tyrosine kinases phosphorylate the protein 18 kDa from complex I, cytochrome c-oxidase, ATP-synthase, protein binding to cAMP/Ca2+ response element, voltage dependent anione channel, steroidogenic acute protein, proapoptotic protein BAD and also other proteins of mitochondrial membranes. Pleiotropy of calcium regulation of mitochondrial functions is proved. The receptors of lipophilic hormone, growth hormone, epidermal growth factor and neurotrophins are discovered in mitochondria. In cellular signaling mitochondria play the integrative role.