• In this study three groups of short children composed of 104 subjects (61 boys, 43 girls) were evaluated for spontaneous secretion of growth hormone (GH). Group 1 consisted of 10 subjects (6 boys, 4 girls) with "classic" GH deficiency. Group 2 consisted of 31 subjects (17 boys, 14 girls) with "nonclassic" GH deficiency. Group 3 consisted of 63 subjects (38 boys, 25 girls) with short normal stature. Blood samples were drawn every 20 minutes over 24 hours, and the mean GH concentration, nocturnal GH concentration, diurnal GH concentration, pulse amplitude, and number of pulses with a GH peak above 5 μg/L were determined. The values for mean height, height velocity, bone age to chronological age ratio, somatomedin C concentration, GH concentration, nocturnal GH concentration, diurnal GH concentration, pulse amplitude, and number of pulses with a GH peak over 5 μg/L were significantly greater in group 3 than in group 2, and these same values, except for the mean diurnal GH concentration, were greater in group 2 than in group 1. The mean GH concentration correlated with the mean nocturnal GH concentration. Subjects in groups 1 and 2 were treated with GH for 1.23±0.53 years (mean ± SD). All the group 1 subjects and 27 (87%) of the group 2 subjects responded with an increase in height velocity greater than 2 SDs per year of therapy. In conclusion, 87% of subjects with a normal GH response to provocative stimuli testing who had a mean height velocity of less than 4 cm/y, mean height lower than the third percentile, mean bone age to chronological age ratio of less than 0.8, and mean GH concentration less than 3 μg/L responded to GH therapy.