The paper describes the Macintosh program MitoProt, which is suitable for studying mitochondrion-related proteins. MitoProt supplies a series of parameters that permit theoretical evaluation of mitochondrial targeting sequences, as well as calculation of the most hydrophobic fragment of 17 residues in the sequence, and a new parameter called mesohydrophobicity. The last two calculations are important for predicting the putative importability of a protein into mitochondria. Taken together, targeting sequence and hydrophobicity characteristics enable one to predict whether a given protein could be mitochondrial when no previous information on the nature of the sequence is available.