In an effort to identify genes that have a major effect on macrophage function during viral infection, we employed differential display reverse transcription (DDRT)-PCR to capture expressed sequence tags (ESTs) of swine alveolar macrophages infected by the porcine reproductive and respiratory syndrome virus (PRRSV). Sequence analyses showed that approximately 60% of these ESTs had significant similarity (≥93%) to known pig ESTs or genes or matched sequences from other species with homology ≥80%. To determine chromosomal localization, PCR-based mapping was performed across either swine somatic cell hybrid or radiation hybrid panels. A total of 48 porcine viral response ESTs were mapped via the swine somatic cell panel or the INRA-Minnesota porcine Radiation Hybrid (IMpRH) panel (LOD > 6.0). Northern blot analyses confirmed PRRSV-induced altered transcript expression for several ESTs, including a 2′-5′ oligoadenylate synthetase and a putative dual-specificity phosphatase. These virus-response ESTs represent good candidate genes for understanding PRRSV pathogenesis and for dissecting host genes which may have major effect on disease resistance.