Somatomedin (Sm) levels throughout pregnancy were determined in a longitudinal study of four normal women and three patients with GH deficiency by use of the RIA for Sm-A, a newly developed RIA for insulin-like growth factor 2 (IGF-2), and the placenta RRA for Sm-A. In both normal women and those with GH deficiency, there was a continuous rise of immunoreactive Sm-A throughout pregnancy. During the third trimester the levels were 2-fold elevated above the level in nonpregnant age-matched normal subjects. No change of immunoreactive IGF-2 levels was found in the normal pregnant women, whereas an increase from low to normal levels was found in GH-deficient patients during pregnancy. The placenta RRA-Sm-A did not detect the increase of Sm-A immunoactivity in the normal pregnant women, whereas the levels were normalized in GH-deficient patients. After delivery a rapid fall of Sm levels occurred in patients with GH deficiency. The calculated half-lives for immunoreactive Sm-A and IGF-2 were 27 and 52 h, respectively. The birth weights of the seven children were significantly (P less than 0.05) correlated to both the individual peak and the mean maternal value of immunoreactive Sm-A during the last trimester. The present findings indicate that the production of both IGF-1 and IGF-2 related peptides during pregnancy is independent of maternal pituitary GH production.