Gliding of red blood cells (RBC) through blood vessels is mediated by the negatively charged glycocalyx located on the surfaces of both RBC and endothelial cells (EC). In various vasculopathies, EC gradually lose this protective surface layer. As a consequence, RBC come into close physical contact with the vascular endothelium. It is hypothesized that the RBC glycocalyx could be adversely affected by a poor EC glycocalyx. This hypothesis was tested by evaluating the RBC and EC surface layers with atomic force microscopy techniques. In the first series of experiments, EC monolayers grown in culture were exposed to rhythmic drag forces exerted from a blood overlay (drag force treatment), and thereafter, the EC surface was investigated in terms of thickness and adhesiveness. In the second series, the glycocalyx of the EC monolayers was disturbed by enzymatic cleavage of negatively charged heparan sulfates before drag force treatment, and thereafter, the RBC surface was evaluated. In the third series, the RBC glycocalyx of the blood overlay was enzymatically disturbed before drag force treatment, and thereafter, the EC surface was evaluated. A strong positive correlation between the RBC and EC surface properties was found (r (2) = 0.95). An enzymatically affected EC glycocalyx lead to the shedding of the RBC glycocalyx and vice versa. It is concluded that there is physical interaction between the blood and endothelium. Apparently, the RBC glycocalyx reflects properties of the EC glycocalyx. This observation could have a significant impact on diagnosis and treatment of cardiovascular diseases.