Abstract Phosphodiesterase (PDE) IV inhibitors have been reported to possess potent anti-inflammatory activities through enhancement of cAMP. In this study, the immunopharmacological effect of PDE IV inhibitor (RP73401) was further carefully evaluated. RP73401 strongly blocked the production of tumor necrosis factor (TNF)-α from lipopolysaccharide (LPS)-stimulated murine macrophages (RAW264.7) and human peripheral blood mononuclear cells (PBMC) and LPS-primed mice. RP73401 did not relieve joint inflammation in adjuvant-arthritis (RA) model, whereas the compound attenuated arachidonic acid-induced inflammation. RP73401 displayed weak or no modulatory effects on the activation of macrophage and lymphocytes (assessed by proliferation, nitric oxide (NO) release and cell–cell adhesion, TNF-α production upon phorbol 12-myristate 13-acetate (PMA) treatment), and fluorescein-isothiocynate (FITC)-induced ear oedema. Collectively, these data suggest that PDE IV inhibitor RP73401 may differentially modulate various immune responses and these may explain its inability to inhibit adjuvant-induced joint inflammation or FITC-induced ear oedema.