This article provides a review of the literature on anteroposterior differences in the growth and functional expression of normal and neoplastic cells. Diverse studies in immunology, wound healing, carcinogenesis, transplantation biology, and developmental biology are brought together to emphasize the practical implications of regional differences for research protocols in all these areas of research. The more fundamental question of mechanisms is approached by consideration of variations in the vascular supply, pattern of nervous system development, expression of temperature differentials, and the establishment of metabolic gradients during development.