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.