No method has yet been available to decode information, hidden in the protein primary structure, on long-range interactions of amino acids. Even a limited amount of information on long-range interactions could help in conformational energy calculations of protein structures and could lead to a better understanding of how the primary structure of proteins determines their conformation. The sequence environments of amino-acid residues were compared from the viewpoint of their participation in long-range interactions. By using the simplest definition, residues were considered as partners in a long-range interaction if they were at least 20 residues apart in the sequence and their C alpha distance was less than 7 A. In spite of this rather crude definition, an analysis of 88 unrelated proteins has shown that the sequence environments (10 residues on each side) of those amino acids which are involved in long-range interactions and of those which are not are significantly different according to the criteria of mathematical statistics. Moreover, in many cases the differences are so pronounced that the involvement of a given amino acid in long-range interactions can be predicted from its sequence environment.