The range of scientific questions utilizing DNA microarray techniques is limited by the fact that these methods require 5-40 microg of high-quality total RNA. Thus, methods that reliably amplify the starting RNA amount could expand the applicability of DNA microarray technology. We developed a single-stranded linear amplification protocol (SLAP) that combines the reproducibility of in vitro transcription and the amplification robustness of polymerase chain reactions. We compared SLAP to the NIH-IVT amplification protocol. SLAP displayed excellent conservation of the 5'/3' signal and demonstrated the most robust amplification, producing the recommended amounts of biotin-labeled RNA with as little as 0.002 microg of starting RNA. Both SLAP and NIH-IVT methods demonstrated good reproducibility, but SLAP maintained the highest level of reliability with RNA starting amounts of <0.05 microg. These results suggest that SLAP is an excellent alternative to IVT-based amplification protocols when RNA is limited by small sample size.