Special problems require special solutions. That is why, despite the trend towards standardization of the procedures in proteomic investigations, a number of alternative protocols, based on 2-DE, have been devised with time and are applied to the resolution of proteins on which the performance of IPG-DALT is poor. The difficult-to-handle samples include high pI, high molecular size and high hydrophobicity proteins. The protocol variants entail changes in the gel media and/or the use of unusual additives (often surfactants or solvents). But also: Specific questions require specific answers. When the aim is not the resolution of individual polypeptide chains in a fully unfolded state but the analysis of higher-order structures (proteins assembled from subunits, complexes assembled from interacting proteins) the standard conditions under which IPG-DALT is performed turn inadequate. Electrophoresis is then performed either in first dimension or in both first dimension and second dimension under non-denaturing (native) and/or non-reducing conditions.