Differential gene expression profiling was performed with a cDNA microarray in the liver tissue of the marine medaka fish, Oryzias javanicus, after exposure to 4-Nonylphenol which is used for detergents, pesticides, anti-oxidants in plastics and rubbers. One hundred ninety-five differentially expressed candidate genes were identified. The expression of 107 genes was up-regulated and that of 88 genes was down-regulated. These genes are associated with the Information storage and processing (Translation, ribosomal structure and biogenesis, J; RNA processing and modification, A; Transcription, K; Replication, recombination and repair, L; Chromatin structure and dynamics, B), Cellular processes and signaling (Cell cycle control, cell division, chromosome partitioning, D; Defense mechanisms, V; Signal transduction mechanisms, T; Cell wall/membrane/envelope biogenesis, M; Cytoskeleton, Z; Extracellular structures, W; Intracellular trafficking, secretion, and vesicular transport, U; Posttranslational modification, protein turnover, chaperones, O), Metabolism (Energy production and conversion, C; Carbohydrate transport and metabolism, G; Amino acid transport and metabolism, E; Nucleotide transport and metabolism, F; Coenzyme transport and metabolism, H; Lipid transport and metabolism, I; Inorganic ion transport and metabolism, P; Secondary metabolites biosynthesis, transport and catabolism, Q), Postics and rubbers. One hundred ninety-five differentially expressed candidate genes were identified. The expression of 107 genes was up-regulated and that of 88 genes was down-regulated. These genes are associated with the Information storage and processing (Translation, ribosomal structure and biogenesis, J; RNA processing and modification, A; Transcription, K; Replication, recombination and repair, L; Chromatin structure and dynamics, B), Cellular processes and signaling (Cell cycle control, cell division, chromosome partitioning, D; Defens2