According to actual conceptions, siRNA enters a multiple-turnover pathway with one siRNA molecule capable of RISC-mediated cleavage of 50 or more mRNA molecules [79] . Even though the fate of steric block oligonucleotides is not really clear, it can be assumed that per splicing event one molecule is used up and translated into a functional mRNA molecule (e.g. single-turnover pathway). As a result the number of molecules needed to trigger an apparent effect is much higher in the splice correction assay compared to the RNAi-based reporter system (confer Table 4 and Table 5 ). On the other hand, being a single-turnover pathway, the splice correction assay should be much more sensitive to even minor changes in intracellular steric block oligonucleotide concentrations whereas the catalytic nature of the multiple-turnover RNAi mechanism might mask such small variations. This is in accordance with the data described above.