Here, we proposed a relative similarity measure to analyze the local or global similarity of DNA sequences. The measure presented in this Letter was based on the Lempel-Ziv complexity. A relative similarity/dissimilarity matrix deduced from the new similarity measure was then outlined to illustrate the similarity of different sequences. As an application of the measure, we analyzed the similarity of the coding sequences of the first exon of beta-globin genes from I I species. (c) 2005 Elsevier B.V. All rights reserved.