Fourteen children between 5 and 12 years old at P1 B1 Tanner's pubertal stage were studied. Seven of them were affected by familiarly short height and seven had a constitutional growth delay. All those patients (responders) except two (hyporesponders) turned out positive to GH stimulation tests (GH to I.T.T., GH to clonidine test). We have treated with clonidine (0.100 mg/m2 for six months) all patients and there were significant results: higher values of basal GH and increase in the response to the clonidine test also in patients hyporesponders before treatment.