Either in children or in adults, arginine (ARG) alone and combined with GHRH (GHRH + ARG) are reliable tests for the diagnosis of GH deficiency. The procedures of these tests generally include GH measurement every 15 min from baseline up to 90–120 min. Aim of our study was to verify if the procedure of these tests could be usefully shortened in clinical practice. To this goal we have studied 173 normally growing children and adolescents (C, 117 M and 56 F, age: 11.3 ± 0.4 yr.) and 125 young and middle aged normal adults (A, 68 M and 57 F, age: 30.0 ± 0.6 yr.). ARG alone test was performed by 81 C and 33 A (0.5 g/kg arginine, iv, from 0 to +30 min, up to a maximum of 30 g) while GHRH (1 μg/kg iv bolus at 0 min) + ARG test was performed by 92 C and 92 A. After ARG alone, taking into account data from +15 to +105 min, GH values above the 3rd centile limit of arbitrary cut-off (7 or 10 μg/1 in C and 5 μg/1 in A) occurred in 85% or 64% and 94% subjects, respectively. After GHRH + ARG test, taking into account only data at +30, +45, +60 min GH values above the 3rd centile limit (20 μg/1 in C and 16.5 μg/1 in A) occurred in 99% of subjects in both groups. Taking into account only these 3 timing points, the percentage of GH peak above the third centile limits after ARG alone was never higher than 60% in C and 85% in A. In conclusion, this study shows that single GHRH + arginine test can be reliably performed in a shortened procedure which makes easier the clinical practice and further reduces costs.