In 59 male and 59 female healthy children of average stature between 7 and 10 yr old, the normal range of plasma somatomedin C was investigated. The 95% tolerance limits narrowed progressively when the child's plasma somatomedin C status was described by the mean of one, two, three, or four determinations at 6-wk intervals. The 95% tolerance limits were therefore based on the mean of four determinations. In 97 children, age 7 to 10, below the 3.0 percentile in height, 44 had an average plasma somatomedin C below the 2.5 percentile. Among these hyposomatomedinemic short children, 19 were partially or totally deficient in growth hormone, 20 had normal immunoreactive growth hormone responses to dopa, glucagon, and sleep (nongrowth hormone deficient), and five had borderline provocative tests. Both growth hormone deficient and nongrowth hormone deficient children showed significant linear growth responses to 6-month courses of human growth hormone (0.16 to 0.70 unit/kg/wk). The responses of the latter group were 50 to 90% as great as those of the former.