A chain with random hydrophobic-hydrophilic charges is studied in the presence of an interface separating a polar from a non polar solvent. Within a Gaussian variational approach in replica space, a transition is found, from a high temperature region, where the chain is delocalized, to a low temperature region, where the chain is localized at the interface. The transition temperature diverges as the neutrality of the chain is approached. Our results are in agreement with an Imry-Ma type argument by Garel et al. [1]. The problem of replica symmetry breaking is also addressed, and the replica-symmetric solution is found to be unstable.PACS numbers: 05.40.+j, 36.20.-r, 87.15.-v Random heteropolymers are often studied in connection with the behavior of complex macromolecules such as proteins [2][3][4]. From a theoretical point of view, random heteropolymers are easier to study, since one can use many tools introduced in the framework of the statistical mechanics of disordered systems. In the case of proteins, it is believed [5,6] that 1