Recently the presence of a coating inhibitory factor was described in human tears which can prevent the binding of proteins to a solid phase. In these earlier studies depositions of lactoferrin and IgG onto plastic was studied. In the study described here, peroxidase conjugated albumin was used as a model to investigate the effect of human tears on the binding of proteins to plastic surfaces. We investigated the question whether contact lens deposits are associated with decreased levels of this factor in the tearfilm of contact lens wearers. The mean value of the coating inhibiting activity in the tears of the controls did not differ significantly from contact lens wearers without deposits. The contact lens wearers with deposits on their lenses, had a lower mean coating inhibiting activity than the contact lens wearers without deposits. No significant difference was seen in coating inhibiting activity in tears obtained from individuals before and after they had worn lenses for three weeks. Also no difference was observed in the coating inhibiting activity on the eyes of persons who were wearing a lens in one eye only. The results of our study show that a too low activity of the coating inhibiting factor in tears is associated with deposits on contact lenses.