Monocytes cultured under serum‐free conditions secreted protein which bound covalently and non‐covalently to agarose beads, an activator of the alternative pathway of complement. There was a significant binding of monoclonal anti‐C3c antibodies, polyclonal anti‐C5, anti‐C6, anti‐C7, anti‐C8, and anti‐C9 antibodies, and of a monoclonal antibody against a neoantigen of polymerized C9 to agarose beads incubated with the monocytes for 24, 48, 72 or 96 h. From these results, we conclude that monocytes produce C5, C6, C7, C8 and C9 that assemble as the terminal complement complex on the surface of the agarose beads. Activation by agarose of the alternative pathway with generation of particle bound C3 and C5 convertases is a prerequisite for the subsequent formation of the terminal complement complex. Whether SC5b‐9 or the membrane attack of complement (C5b‐9) is formed on the beads will be examined.