Matrix metalloproteinases (MMPs) are involved in tissue destruction in allergic airway diseases. We studied the ability of various allergenic substances to directly activate recombinant 92 kDa proMMP-9. The substances included hay dust suspension (HDS) and its components (supernatant, particulate matter and wash fluid of particulate matter), storage mite extract and two Aspergillus fumigatus extracts. The allergen suspensions were incubated in vitro with proMMP-9. After incubation the conversion of proMMP-9 to 10 kDa lower active forms were studied using gelatin zymography and Western immunoblot quantified by computerized densitometry. All studied allergens except HDS significantly and efficiently activated proMMP-9 as compared to a negative control. At the concentrations employed, the most potent activators were A. fumigatus extracts and mite suspension. The greater potency of mite and fungi as proMMP-9 activators suggests that these allergens may be more damaging to airways even at low concentrations. (C) 2005 Elsevier B.V. All rights reserved.