Flow cytometry and cell-based enzyme-linked immunosorbent assays have been used to detect surface proteins on cells. A recently available electrochemiluminescent assay methodology using carbon surface electrodes built into the bottom of microwell plates can be used as an alternative to these methods and has some advantages. The carbon surface plates bind suspension cells tightly enough to allow plates to be washed using a plate washer. This eliminates the centrifugation steps typically used for washing suspension cells. For adherent cells, human umbilical vein endothelial cells can be grown, activated, and assayed in the same carbon surface plate. This eliminates the need to detach cells from tissue culture plates for analysis, making the electrochemiluminescent assay much easier to perform than a corresponding flow cytometry assay. This electrochemiluminescence technology provides a high throughput method to detect surface proteins on live cells.