Circulating levels of IGF-I, two key binding proteins, and insulin as determined by RIA for patients with PV and normal individuals. Data from two separate experiments (experiment no. 1 [○, •] and experiment no. 2 [□, ▪]) compare plasma levels of IGF-I in micrograms per liter (A), IGFBP-3 in milligrams per liter (B), IGFBP-1 in micrograms per liter (C), and insulin in picomoles per liter (D) for age- and sex-matched normal individuals (N) and patients with PV. Each point represents one individual, whereas the horizontal bars indicate the median value for each group. Levels of IGF-I, IGFBP-3, and insulin are normal in patients with PV, but their IGFBP-1 levels are significantly elevated.