Veterinary pathologists engaged in basic research use a variety of methods to study disease pathogenesis at the light microscopic and submicroscopic (protein and mRNA) levels. The ribonuclease protection assay is a sensitive and accurate method to measure mRNA expression. The major advantages of the assay are that multiple mRNA species can be measured simultaneously in a single total RNA sample and that the assay has relatively high throughput. The major disadvantage is that the assay requires moderate technical skill.