Activation of complement leads to the generation of C3a and C5a inflammatory peptides. C5a is a potent chemotactic factor, stimulating the secretion of proteolytic enzymes by neutrophils and osteoclast activating factor/Interleukin-1 by monocytes. In vitro generation of C3a and C5a was measured by radioimmunoassay techniques. The results showed significant complement activation by all implants tested when compared to the control serum incubation. It is concluded that all of the implants studied activated the complement system and are not physiologically inert. Complement activation, therefor, may contribute either positively to healing or negatively to a poor outcome in osseoadaptation initially or over time. Schlagwörter: complement, implant, Interleukin-lß, osseoadaptation