Several technical papers have been published describing tests of concretes containing metakaolin, mainly showing enhanced strength development and durability. We conducted a similar range of tests to evaluate the new source of metakaolin, and also developed a mix design that benefits from the lower water requirement of a binder containing fly ash, metakaolin, and portland cement. We used four test mixes: a control without supplementary cementing materials, MK with 7% metakaolin, SF with 7% silica fume, and FA with 20% fly ash and 5% metakaolin. We found that, with a binder containing cement, metakaolin, and fly ash, producers can make a concrete with enhanced durability at little or no extra cost over a regular-cement mix. In addition, concrete made with metakaolin as a cement extender developed slightly higher strengths at early ages and similar strength at later ages, when compared with the SF mix. Also, the durability of the FA mix was similar to that of the MK and SF mixes; however, the strengths of the FA mix concretes were lower. Finally, increasing amounts of metakaolin reduced ASR expansion in concretes made with a reactive aggregate. For a full-length version of this article for research on metakaolin, call 630-705-2623. Keywords: metakaolin, Construction Technology Laboratories, Taylor, Burg, fly ash, supplementary, cementitious, material, durable, cement, perform, chloride, ASR