By covalently coupling L-lysine to an analytical surface through a dipeptide linkage such that the epsilon-amino group is accessible, we have looked at plasminogen binding in real time. The results have led to a model of plasminogen interactions with epsilon-amino groups, This paper focuses on the desorption kinetics of plasminogen adsorbed to this material, Plasminogen is shown to bind to the dipeptide in at least four different ways to the epsilon-amino groups. It is suggested that some molecules bind to several epsilon-amino groups at the same time. The surface plasmon resonance analysis also indicates that the interaction of Glu-plasminogen with L-lysine is very complex and may not be defined simply by discrete kringle interactions alone, Dissociation constants ranging from 0.1 s(-1) to less than 5 x 10(-7) s(-1) are observed. This material may well represent a surface sufficiently similar as to mimic plasminogen binding to fibrin.