Serum somatomedin B (SmB) levels in cirrhotic individuals, 3.3 +/- 1.5 mg/l, were strikingly lower (P less than 0.001) than in normal subjects, 9.0 +/- 1.7 mg/l. SmB levels were clearly related to the levels of alpha 2-globulins in the cirrhotics (r = + 0.8, P less than 0.002). Serum SmB and growth hormone correlated negatively in a group of normal and cirrhotic individuals (r = -0.67, P less than 0.001). Direct measurements of serum SmB failed to reveal differences between hepatic, renal and peripheral veins. These findings suggest that: 1) SmB is produced by liver and/or normal liver function plays an important role in maintaining normal serum SmB levels; 2) SmB carrier proteins are reduced in the cirrhotics and 3) SmB is part of a negative feed-back system involving growth hormone.