Matrix metalloproteinases are particularly potent in degrading basement membrane collagen and other extracellular matrix components. We have investigated the effects of a selective phosphodiesterase 4 inhibitor, RP 73-401 N-(3,5-dichloropyrid-4-yl)-3-cyclopentyloxy-4-methoxybenzamide, on gelatinase (matrix metalloproteinase-2 and matrix metalloproteinase-9) activity in ovalbumin-sensitized and -challenged mice. Twenty-four hours after the last challenge, matrix metalloproteinase activity was evaluated in the bronchoalveolar lavage fluids by a zymography technique, and a significant increase in matrix metalloproteinase-9, but not matrix metalloproteinase-2, activity was noted. When administered orally (0.3–3 mg/kg) 1 h before each ovalbumin challenge, the selective phosphodiesterase 4 inhibitor, RP 73-401, significantly reduced this increased matrix metalloproteinase-9 activity in bronchoalveolar lavage fluids. Our data suggest that RP 73-401 may modulate tissue remodelling associated with lung inflammatory processes including asthma.