The complement activation potential of surface modified (passivated) poly(methyl methacrylate) (PMMA) intraocular lenses (IOLs) with polypropylene loops was compared to that of standard PMMA IOLs with polypropylene loops. Both lens types were incubated in human sera for six hours and then the C3a and C5a levels were measured by radioimmunoassay. Sera incubated with either IOL type generated significantly higher levels of C3a and C5a than control sera incubated without any IOL. The amount of C3a and C5a generated by the passivated PMMA IOLs was comparable to the levels generated by the standard PMMA IOLs. The results of this study show that surface passivated PMMA IOLs with polypropylene loops activated complement to the same level as standard PMMA IOLs with polypropylene loops.