Two male patients with achondroplastic dwarfism aged 7-5/12 and 14½ years were treated with human growth hormone 5 mg daily. Both showed nitrogen retention on balance studies, the older second patient to a marked degree. In the younger patient, height increased from 95.4 to 106.3 cm on hgh 5 mg daily alone for 14 out of 24 months. The rate of growth approximately doubled during the first two treatment periods as compared with the pre-treatment rate. In the second older patient hgh was administered 5 mg daily intramuscularly for 21 out of 33 months. Growth from 129.6 cm to 137.8 cm occurred with the rate increasing following the addition of Na-1-thyroxine to the routine. This increased growth rate occurred during the post-puberty deceleration phase. Bone ages, interpreted from changes in the phalanges and metacarpals, increased from 4½ to 6 years during 16 months in Case 1, and from 13½ to 18 years in 33 months in Case 2. Transient adolescent gynecomastia appeared in Case 2. No local or general toxic effects were noted.