Suppression subtractive hybridization (SSH) was used to generate a subtracted cDNA library enriched with gene transcripts differentially expressed in the spleen of orange-spotted grouper Epinephelus coioides after 5 days of infection with Singapore grouper iridovirus (SGIV). In the forward and reverse-subtracted libraries, 260 and 153 non-redundant expressed sequence tags (EST), respectively, were identified. These annotated genes responding to SGIV infection were grouped into eight gene categories related to immunity, cell structure, transcription-translation, cell signalling, metabolism, mitochondrial proteins, ribosomal proteins and unknown or hypothetical proteins. A DNA microarray containing all the differentially expressed genes was constructed, and the gene expression patterns in different tissues were investigated in virus-infected E. coioides. Of these genes, four associated with the infection processes were identified and further investigated by quantitative real-time PCR. These results provide new insights into the molecular basis of host-pathogen interactions in E. coioides, and will help the development of control strategies against SGIV infection.