Three European biological control agents of the exotic, wetland, perennial plant purple loosestrife,Lythrum salicariaL., were released in North America in 1992 and 1993. Two leaf-feeding beetles,Galerucella calmariensisL. andG. pusillaDuftschmidt, from 2 climatically different source populations in Germany, were released in 10 different states and 6 Canadian provinces. The importance for establishment success of climatic preadaptation, number of individuals released, release of laboratory or field-collected material, and confinement of release were investigated in a series of experimental releases. BothGalerucellaspecies became established at all 1992 release sites regardless of their origin or release method. Higher survival in cages was found for releases of 600 beetles compared with releases of 200 beetles. The amount of litter, number of standing dead stems, or host-plant density clid not affect establishment. A root-feeding weevil,Hylobius transversovittatusGoeze, was released in 9 states and 2 Canadian provinces, and established in the field in 6 states and both provinces. The 3 species successfully passed the most critical phase for establishment in North America; production of the generation following release.