Connective tissue turnover plays a prominent role in tumour growth and metastasis. We followed serum levels of seven connective tissue parameters in 37 patients with colorectal cancer metastatic to the liver prior to and during chemotherapy. Serum samples with episodes of tumour control (n=112) showed an increase of matrix metalloproteinase-2 (MMP-2) (P<or=0.01) and a decrease of tissue inhibitor of MMPs (TIMP-1) levels (P<or=0.01), while serum samples with episodes of tumour progression displayed the reverse pattern (P<or=0.01 and P<or=0.05, resp.). The ratio of circulating MMP-2/TIMP-1 was also significantly higher in episodes of tumour control vs tumour progression and prior to treatment (P<or=0.0001). We conclude that serum MMP-2 appears to reflect tumour resorption, while serum TIMP-1 may mirror tumour expansion.