AbstractInsulin-like growth factors (IGF) I and II are chemically-related single-chain peptides with diverse actions on cellular growth and metabolism. This review will focus on recent information pertinent to the biochemical and molecular biological aspects of these peptides. Three areas will be examined: The structure of the two IGF molecules and their precursors will be analyzed; the complicated anatomy of the IGF genes and their mRNAs will be described; and the multiple ways in which the expression of IGF-I and IGF-II can be regulated will be discussed. Gaps in our understanding of these peptides will be highlighted in the context of opportunities for further investigation in this field.