Selenium is an essential trace element although at higher doses it is also known to be a toxic agent causing a wide range of symptoms including growth retardation. In order to investigate the effect of sodium selenite on growth, insulin-like growth factor-binding proteins (IGFBPs) and insulin-like growth factor-I (IGF-I), 30 male Wistar rats were randomized into three groups. Group A was treated with sodium selenite in the drinking water (3.3 mg selenium/l). Group B was ad libitum fed with free access to standard fodder and tap water and group C was pair fed relative to the selenium-treated rats. Serum IGF-I and IGFBPs were determined on days 0, 14 and at the end of the study on day 35. Selenium-treated rats had significantly lower body weights compared with group B rats on day 9 and group C rats on day 14 (P < 0.05). Tibia length was measured at the end of the study and no difference was observed between groups B and C (3.77 +/- 0.04 cm vs 3.60 +/- 0.02 cm); however, selenium-treated rats had significantly shorter tibia lengths (3.46 +/- 0.03 cm) compared with rats in groups B (P < 0.001) and C (P < 0.05). Selenium treatment induced a significant reduction in circulating IGF-I by the end of the study compared with ad libitum and pair fed rats (P < 0.05). Serum subjected to Western ligand blots showed four distinct IGFBP bands with apparent relative molecular weights of 38-47 kDa (doublet) (IGFBP-3), 30 kDa (IGFBP-1 and/or IGFBP-2) and 24 kDa (IGFBP-4).(ABSTRACT TRUNCATED AT 250 WORDS)