In conclusion, our data show that hairpins of various base composition in stem and loop can act as efficient frameshift stimulators. Combined with previous studies on antisense-induced frameshifting (43, 44) , these data support the notion that downstream structures primarily serve as barriers to stall translating ribosomes to stimulate frameshifting. Although there exists a linear relationship between calculated stability and frameshifting, local destabilizing elements like bulges or mismatches in a hairpin can greatly influence frameshift-inducing activity. Future experiments addressing the mechanical strength of these hairpins (7-9) may help to improve our understanding of the basics of ribosomal frameshifting. Usefulness of Published PCR Primers in Detecting Human Rhinovirus Infection We conducted a preliminary comparison of the relative sensitivity of a cross-section of published human rhinovirus (HRV)–specific PCR primer pairs, varying the oligonucleotides and annealing temperature. None of the pairs could detect all HRVs in 2 panels of genotyped clinical specimens; >1 PCR is required for accurate description of HRV epidemiology. H uman rhinoviruses (HRVs) cause more asthma exacerbations than any other known factor, in addition to causing most colds and infl uenza-like illnesses. The prevalence of HRV in published reports varies considerably. A novel HRV clade identifi ed in 2006, now known as HRV species C (HRV-C) (1), can be identifi ed only by PCR. Since 1988, seasonality and clinical outcomes and numerous different primer pairs have been used to identify HRV; how well these methods perform on new HRV types is uncertain. Given the likely variation in the preparation of RNA, the quality and formulations of commercial reverse transcription (RT)-PCR enzymes and reaction mix components and changes in thermal cyclers since 1988, not surprisingly many, perhaps most, of these assays are not being used in the manner they were originally described. For example, the fi rst HRV-specifi c primers reported (2) have subsequently been used with different RNA preparation methods, amounts of reverse transcriptase, cDNA priming strategies, dNTP concentrations, annealing temperatures (T M s), and cycling conditions (3, 4) .