An analysis of the sequence information contained in a compilation of published binding sites for E. coli integration host factor (IHF) was performed. The sequences of twenty-seven IHF sites were aligned; the base occurrences at each position, the information content, and an extended consensus sequence were obtained for the IHF site. The base occurrences at each position of the IHF site were used with a program written for the Apple Macintosh computers in order to determine the similarity scores for published IHF sites. A linear correlation was found to exist between the logarithm of IHF binding and functional data (relative free energies) and similarity scores for two groups of IHF sites. The MacTargsearch program and its potential usefulness in searching for other sites and predicting their relative activities is discussed.