Abstract: Abstract Suppression of the hapten-specific response to a hapten-carrier conjugate was seen when the conjugate was injected either together with another hapten conjugated to an homologous carrier or together with the homologous unconjugated carrier. Simultaneous injection of non-immunogenic, unconjugated hapten did not suppress the anti-hapten response to a different hapten conjugated to a carrier. Preimmunization with unconjugated carrier, which augments the carrier-specific response, suppressed the hapten-specific primary response to a hapten-carrier conjugate and enhanced the degree of competition seen when two hapten-carrier conjugates were given simultaneously.