Over the last several years, the authors have studied the relationship of insulin-like growth factors (IGFs) and the insulin-like growth factor binding proteins (IGFBPs) in the circulation in a number of clinical settings. Patterns have emerged that seem to be characteristic of various conditions. In aging, there are marked decreases in IGF-I and -II, normal levels of IGFBP-3, and marked increases in IGFBP-1 in serum. Using ligand blotting and an IGFBP-3 proteolysis assay, BP-3 is intact. Based on native gel electrophoresis, IGFBP-1 is in its most highly phosphorylated state in those elders who have high IGFBP-1 levels. This pattern is slightly different in catabolic conditions such as AIDS (wasting in adults; failure to thrive in children), uncontrolled diabetes mellitus, trauma, and severe burns. In these conditions, serum levels of IGF-I and -II are markedly diminished, IGFBP-3 levels are also decreased, and IGFBP-1 levels are markedly increased. In addition, there is increased proteolysis of IGFBP-3 (AIDS failure to thrive, uncontrolled diabetes mellitus) and disruption of the ternary complex with decreased levels of ALS (AIDS wasting and burns). IGFBP-1 is in its most highly phosphorylated state in all catabolic conditions studied. Thus, the alterations in the circulating levels of IGFs and the changes in the physical state of the IGFBPs may lead to decreased anabolic activity and be a part of the mechanism of increased catabolism and wasting.