Type IV and interstitial collagenolytic activities were compared in human malignant and normal trophoblast cells cultured on plastic, in presence or absence of laminin in solution, on matrigel (a gel of basement membrane components) and on type I collagen gel. Laminin highly stimulated the type IV collagenolytic activity but not the interstitial collagenolytic activity, in malignant trophoblast cells. This glycoprotein had no effect on the interstitial collagenolytic activity and doubled the type IV collagenolytic activity in normal trophoblast cells. Thus malignant trophoblast cells produce preferentially the enzyme able to degrade basement membrane when in contact with laminin, and the enzyme able to degrade interstitial collagen fibers when cultured on type I collagen. On the contrary, type I collagen gel and matrigel equally increased both type IV and interstitial collagenolytic activities by normal trophoblast cells. Interactions of tumor trophoblast or normal trophoblast cells with the extracellular matrix result thus in distinct stimulations of collagenolytic activities. Increased production of type IV collagenolytic activity upon exposure to laminin appears to be specific of the metastatic phenotype.