Effectiveness of growth-promoting therapies. Comparison among growth hormone, clonidine, and levodopa. The ability of growth hormone, clonidine, and levodopa to stimulate growth was compared in short and slowly growing children randomly assigned to different treatment regimens for 6 months. There were 10 children in each group, and 10 additional subjects served as controls. Growth hormone improved mean height velocity, height velocity SD score, and height SD score. The mean height velocity and height velocity SD score were significantly increased by clonidine, while levodopa only enhanced the mean height velocity SD score of the treated children. Moreover, in nine patients (90%) receiving growth hormone, two (20%) receiving clonidine, and one (10%) receiving levodopa, the height velocity was raised by more than 2 cm/y. The increments in height velocity and height SD score were greatest in the growth hormone group. Clonidine induced an increase in height velocity significantly different from that in control children only. In the control group, there was a significant reduction of height SD score with time. 