Evaluation of growth hormone dependent IGFBP3, stable in time and with no circadian variations is a useful parameter for diagnosing growth hormone deficit. The IGFBP3 was evaluated using sera, collected and kept at -20 degrees C, from subjects classified according to auxologic characters and response sup. or inf. to 8 ng/ml GH after two stimulation tests and median nocturnal GH sup. or inf. to 3 ng/ml. Two groups were studied: 1) Small stature GHD (growth hormone deficiency): 14 cases; 2) Constitutional small stature (RCC,BSF): 12 cases. A third group composed of 8 normal height, weight and disease-free children formed the control group. The IGFBP3 values were below the 5th percentile in 86% of GHD cases, between the 5th and 95th percentile in 66.6% of constitutionally short stature children and in all normal controls was about the 50th percentile. The IGFBP3 also shows a statistically significant correlation between median nocturnal GH, both in deficient and constitutionally short stature groups (p < 0.01).