The time-dependent binding probabilities are reported for three different cell configurations. A, background-corrected data show the adhesion probability versus contact time between RBCs modified identically with CEC1–5 His6 at densities of ~4 (black squares) and ~5 (black circles) cadherins/μm2. B, measurements between identically modified CEC1–5 Fc RBCs at 39 cadherins/μm2 (white squares) and 12 cadherins/μm2 (white circles). C, measurements between C-CHO and CEC1–5 Fc RBCs. The cadherin densities on the C-CHO and RBCs were, respectively, 10 and 12 cadherins/μm2 (black squares) and 1 and 38 cadherins/μm2 (black circles). The data also show the blank (white squares) and EDTA control (white circles).