Translation of genetic information into proteins is a fundamental cellular process essential for all life. Accurate protein synthesis relies on the integrity of the RNAs (mRNAs, rRNAs and tRNAs) in translational complexes. Of these RNAs, systems that respond to mRNA abnormalities have been well characterized in both prokaryotic and eukaryotic cells. It is becoming apparent that eukaryotes also possess pathways to detect and eliminate defective tRNAs. However, prior to the work presented here it was unknown whether cells exert quality control over their mature rRNAs, despite this RNA being the most abundant in the cell. To address this question, rRNAs with point mutations in regions of either the 18S rRNA important for codon decoding or the 25S rRNA important for peptide bond formation were introduced into yeast. Unlike mRNA coding genes, which in yeast are generally present in single copies, there are as many as 200 copies of the rDNA genes per cell. Thus, expression of mutant rRNAs from chromosomal rDNA genes was problematic. To overcome this, a method utilizing existing plasmid rDNA reporters was developed to express and specifically detect mutant rRNAs in yeast. Using this system led to the discovery of a eukaryotic rRNA surveillance pathway, nonfunctional rRNA decay (NRD), that eliminates mature but defective rRNAs of ribosomes and ribosomal subunits in S. cerevisiae . Further characterization of NRD revealed the mechanism by which mutant 18S rRNAs are eliminated is quite different from mutant 25S rRNA elimination, dividing the pathway into 18S and 25S NRD. Together the experiments presented here have contributed to our understanding of RNA surveillance in eukaryotes. In the current model, mutant 25S rRNAs are degraded as part of free ribosomal subunits outside of translational complexes, and mutant 18S rRNA decay occurs during translation elongation. That 18S NRD also utilizes certain mRNA decay proteins suggests the entire translational complex is both monitored and subject to elimination if found defective during protein synthesis.