The stimulatory effect of L-Dopa and L-Carbidopa (Nacom) on HGH secretion was determined in 12 children of normal height aged from 6 to 14 years. Each child received a standard dose of 250 mg L-Dopa and 25 mg L-Carbidopa p.o. HGH concentration in the serum was determined at standard intervals. All subjects showed a sufficient increase of HGH. The mean value was 19.6 ng/ml. According to the maximum values of the HGH concentration the sample can be divided into two groups; the first group reached the highest values after 20--40 min, the second one after 60--90 min. On evaluation of the curve of the mean values it appears that 2 blood samples taken 40 and 90 min after the ingestion of L-Dopa and L-Carbidopa are sufficient in order to exclude HGH deficiency. The theoretical background for HGH secretion after stimulation by L-Dopa and L-Carbidopa is discussed.