In post-genomic era, a plethora of protein structures have been solved but the functions of some of them are unknown. In this context, the role of hydropathy index of amino acids in predicting the function of a structurally known and functionally unknown protein was explored. Initially serine protease class was taken for analysis. Various methodologies like calculation of average hydropathy index for a five-residue window of a given sequence, hydropathy cluster analyses, etc., were done. Among these, the distribution of hydropathy clusters seems to suggest that the location of these clusters is conserved for a given class of proteins. Hence, this methodology was extended to different classes of proteins and to a protein with unknown function. (C) 2004 Elsevier Inc. All rights reserved.