It has been reported that insulin-like growth factor (IGF) II is associated with human primary colorectal tumors and colon-carcinoma cell lines. Here, we examine alterations in circulating levels of IGFs and IGF binding proteins (IGFBPs) in patients with colorectal carcinoma, and compare them to age- and nutrition-adjusted references. We report (i) an increase in serum IGF-II concentrations (about 2-fold), whereas IGF-I concentrations are regarded as normal when aging is taken into account; (ii) an apparent increase in serum IGFBP-3 levels when compared to those of healthy elderly subjects, IGFBP-3 only being detected in the 150-kDa IGFBP ternary complex as in normal serum; (iii) abnormally elevated serum IGFBP-2 levels taking into account the apparent concentrations of IGFBP-3. This simultaneous elevation of IGFBP-3 and IGFBP-2 in the serum of patients with colorectal tumors appears to be unique in that it reflects a break in the inverse relationship between the serum IGFBP-3 and IGFBP-2 levels that is observed in normal and in several physiopathological conditions. Moreover, it enables a distinction to be made between 76.5% (13/17) of patients with colorectal carcinoma and normal adults, age-related healthy aged and malnourished patients. We propose that the disturbed serum IGFBP profile observed in the patients with colorectal cancer may be a consequence of oversecretion of IGF-II by the tumor cells. The usefulness of IGFs and IGFBPs as potential colorectal tumor-associated metabolic markers should be further investigated.