Growth factors secreted by either host or tumour cells play a major role in tumour cell progression. Besides stimulating cell division, growth factors may also stimulate cell migration and modulate matrix metalloprotease (MMP) production. MMPs are enzymes involved in a variety of physiological and pathological processes including tumour cell invasion and metastasis. We have previously shown that different growth factors regulate the motile behaviour of human lung cancer cell lines. In order to further advance our knowledge of the role the different growth factors play in lung cancer, we investigated their effect on two key enzymes belonging to the MMP family of enzymes, namely MMP-9 and MMP-2. Serum-free cultures of three human non-small cell lung cancer cell lines were exposed to five different growth factors: insulin-like growth factor I (IGF I) and II (IGF II), hepatocyte growth factor (HGF), epidermal growth factor (EGF) and stem cell factor (SCF). The expression of MMP-9 and MMP-2 in growth factor-treated and untreated cell lines was evaluated using gelatine zymography and quantified using computer-assisted image analyses. We found heterogeneous expression and activity of MMP-9 and MMP-2 in all three lung cancer cell lines. The most important finding in our study is that HGF and EGF are capable of stimulating the conversion of MMP-9 from a latent to an active form in human large cell lung cancer cell line U-1810 [corrected]. IGF I, IGF II, HGF and EGF stimulated an enhanced expression and activity of the latent form of MMP-2 and MMP-9. SCF did not enhance MMP activity in any of the cell lines tested. Our previous studies have shown that IGF I, IGF II, HGF, EGF and SCF induce migration of human non-small cell lung cancer cells in the presence of extracellular matrix (ECM) components. In the present study we show that growth factors can also enhance the expression of MMP's in these cells. Taken together these results indicate that certain growth factors may promote invasiveness through their ability to induce not only cell migration, but also by enhancing the expression and activity of matrix degrading MMP-2 and MMP-9.