Laminin is a large multidomain glycoprotein with diverse biological activities which include stimulation of neurite outgrowth, enhancement of tumor metastasis, and promotion of cell growth, adhesion, and differentiation. A 19 amino acid synthetic peptide derived from the E8 fragment of the laminin A chain (Cys-Ser-Arg-Ala-Arg-Lys-Gln-Ala-Ala-Ser-Ile-Lys-Val-Ala-Val-Ser-Ala-Asp -Arg- NH2) was identified which promotes metastasis and stimulates collagenase IV activity in the culture medium of B16 melanoma cells (Kanemoto et al., 1990). We report that this peptide, here designated LamA2091-2108, is also a potent stimulator of tissue plasminogen activator (t-PA)-catalyzed plasminogen activation, resulting in a 22-fold increase in the kcat/Km of the activation reaction. The activity of purified type I and type IV collagenase was inhibited by LamA2091-2108 with IC50 values of 3 and 43 microM, respectively. These data support an alternative mechanism for the appearance of collagenase activity in the culture media of melanoma cells, namely, that the peptide stimulates plasminogen activation, subsequently generating collagenase activity.