Nonsense mutations cause approximately 10% of genetic disease cases. Certain molecules can rescue the expression of genes carrying a nonsense mutation, either by activating readthrough of the premature termination codon or by inhibiting the mRNA surveillance mechanism called nonsense-mediated mRNA decay (NMD). In the first approach, a full-length protein will be synthesized, differing by at most one amino acid from the wild-type protein. In the second approach, a truncated protein will be synthesized, which sometimes retains partially or completely the function of the wild-type protein. Here we describe methods for identifying, by screening, molecules having the capacity either to inhibit NMD or to activate readthrough.