The mechanism of quenching to tryptophan fluorescence was studied for a number of proteins and membranes of sarcoplasmic reticulum. The inductive-resonance energy transfer from tryptophanyls to pyrene was shown to be absent though all the necessary and sufficient Förster's conditions were met. The quenching proceeds by a dynamic mechanism. The quenching efficiency characterises the sterical accessibility of tryptophanyls for pyrene. The simultaneously observed rise of luminescence of the quencher is trivial. It was concluded that measuring intermolecular distances and defining protein conformational states using Förster's theory is wrong in case of the tryptophany-pyrene pair.