An efficient technique using hydrazine (N(2)H(4)) vapor as an agent for the rapid reduction of high-density layers of catalytic nanoparticles is demonstrated. With as little as 10 mTorr hydrazine bled into a thermal chemical vapor deposition (CVD) apparatus, efficient reduction of metal-oxide catalyst particles is achieved more rapidly than when using atomic hydrogen as the reducing agent. Postreduction catalyst imaging emphasizes the differences in nanoparticle formation under different reduction environments, with the most uniform and compact catalyst size distribution observed following hydrazine exposure. Low-temperature reduction studies suggest that as little as 15 s N(2)H(4) exposure at temperatures of 350 °C can yield a reduced catalyst layer preceding the synthesis of dense, aligned arrays of single-walled carbon nanotubes (SWNT) with uniform height. This work demonstrates a simple route toward scalable, vapor transport reduction of metal-oxide catalyst relevant to a number of catalytic applications, including the synthesis and selective synthesis of aligned SWNT arrays.