At the moment the most studied are the folding and unfolding processes of the apoform of this protein at different denaturant concentrations, various pH values and temperature. It was shown that the folding of this protein occurs via the formation of an intermediate state of the molten globule type and can be described using a twostage sequential scheme of reaction. It was demonstrated using the stopped-flow and quench-flow techniques that ureainduced apomyoglobin refolding goes via a kinetic intermediate that forms within 6 msec and is structurally similar to the equilibrium molten globule intermediate observed at pH 4.2. Subsequent kinetic studies suggested that this intermediate is onpathway. Quench-flow amide proton exchange combined with mass-spectrometry confirmed that apomyoglobin folds by a single pathway and that the intermediate is obligatory. In general, the formation of the molten globule state of apomyoglobin proceeds very rapidly during the burst-phase within several msec, which is in the range of the dead time of the instruments use. Therefore, in kinetic experiments it is almost impossible to detect the molten globule state of apomyoglobin. However, the rapidly formed molten globule state affects the parameters characteristic of the following stages of protein folding. The approach that allows taking into account the effect of the fast folding stage of protein folding on the rate of the slow folding stage of this protein is theoretically grounded. This approach permits one to obtain population values of the protein molten globule state versus the denaturant concentration, i.e. to study the stability of the molten globule state, and using the kinetic data of chevron plots it is possible to design the energy landscape of apomyoglobin. The effect of substitutions of different amino acid residues on the native state of apomyoglobin is studied quite well. Analogous experiments were performed with other proteins as well. The effects of substitutions of different amino acid residues on the stability and the rate of native state formation in various proteins have been studied systematically. Thus, for some proteins the so-called folding nucleus has been determined with the Q-analysis. The folding nucleus includes amino acid residues and protein parts the substitutions of which affect the folding/unfolding rate of the protein native state. In some cases, such studies involve several dozens of mutant proteins with single substitutions of amino acid residues. This permits revealing the localization of residues that determine the rate of formation and the stability of the protein native state. Nevertheless, there are virtually no investigations employing multiple substitutions of amino acid residues for analyzing intermediate states of proteins, although intermediate states of some proteins are functionally important and in many respects determine the properties of proteins.