We have developed a sensitive and specific sandwich type enzyme-linked immunosorbent assay (ELISA) to detect type IV collagenase (MMP-2) in human plasma which employs the combination of affinity purified rabbit polyclonal antibodies and mouse monoclonal antibodies to human MMP-2. The MMP-2 ELISA detects latent and activated MMP-2, MMP-2 complexed with TIMP and MMP-2 complexed with alpha 2 macroglobulin (65% efficiency). To determine whether physiologic conditions associated with increased connective tissue turnover are accompanied by increased MMP-2 levels in plasma, we compared enzyme levels in pregnant and nonpregnant women. Plasma MMP-2 (mean +/- standard deviation) was significantly increased (p less than 0.05) in the second half of pregnancy (650 +/- 312) as compared to early pregnancy (356 +/- 139) or the nonpregnant state (387 +/- 193). As a result of the linkage between type IV collagenase production by cancer cells and the metastatic phenotype, the assay of MMP-2 in plasma is of potential clinical value in cancer.