Abstract.An immunoblotting technique allows direct visualization of Chido and Rodgers antigenic determinants on intact C4 proteins. C4 molecules separated by electrophoresis are selectively transferred to nitrocellulose membranes saturated with goat antiserum to human C4. The membranes are then incubated in alloanti‐Chido or anti‐Rodgers followed by enzyme‐conjugated goat antihuman IgG. Molecules with Chido or Rodgers reactivity are visualized by incubation with an indicator substrate for the bound e