In Ontario, serious difficulties are frequently encountered in the establishment of young peach trees as replacements in old orchard sites. Symptoms vary from slight stunting to complete absence of growth. Causal factors described in conflicting reports in literature on the subject and information gained from examination of affected trees attest to the complexity of the problem. The failure of the replanted trees has been ascribed to the activity of insects and nematodes as well as to the effect of nutritional disturbances, toxic agents, and spray residues. The problem is being studied as a co-ordinated investigation by plant pathologists, entomologists, microbiologists, horticulturists, nematologists, and chemists. The account given here is introductory to a series of papers dealing with the various phases of the investigation and includes mainly a review of the literature and a description of the symptoms and effects of the disorder.