The objective of this study is to screen the differential gene expression in response to a pathogenic infection in the skin of fish, and to provide a basis for understanding the fish skin immune mechanism at the molecular level. The immune response in the skin was analyzed by using induced zebrafish as a model, and applying the affymetrix zebrafish cDNA microarray hybridized to the skin tissues. Total RNAs were isolated from the skin tissues of adult fish, labeled with biotin, and hybridized to zebrafish cDNA gene chips. The expression profiles from the hybridization to 15 617 genes in the zebrafish cDNA array were analyzed by the GeneChip Operating Software (GCOS1.4). Out of 15 617 genes in zebrafish cDNA chips, a total of 175 was identified to be significantly expressed in the skin tissues, of which 150 were up-regulated and 25 were down-regulated. Among the 150 up-regulated genes, the functions of 91 genes were known and 59 were unknown. Furthermore, by using the Gene Ontology (GO) method the differential expression genes could be categorized into 13 functional groups, and some of them are considered as potential candidates in the fish skin immune response. Thus, several genes related to immune response in the skin were identified, including major histocompatibility complex class I genes (UEA, UFA), complement component (C1q, C7-1), lectin (HBL3, LGALS1L3), early growth response 1 (EGR-1), tumor necrosis factor superfamily (TNFSF10L4), coagulation factor V(F5), transferrin-a (TF-a), and several proteases. The Affymetrix zebrafish cDNA microarray is useful for identifying the functional genes involved in the skin immune defense of fish: that is, MHC I, complement, lectin, and proteases. However, future analysis of the function of these genes may contribute to an understanding of the mechanisms of pathogenesis