Twenty patients with rheumatoid arthritis or Still's disease associated with growth failure were treated with human growth hormone, 7.5 to 17 U/m2 body surface per week. Five patients did not respond with better growth. In the remainder the mean growth rate increased from 1.9 cm/year (range: 0 to 3.3) to 6.2 cm/year (range: 3.6 to 12) over 5 to 7 months. Twelve patients treated for longer periods increased their mean growth rate from 2.6 cm/year (range: 0.7 to 5.7) to 6.3 cm/year (range: 2.4 to 9.7) and continued to grow during a second year of treatment. Growth velocity decreased in 6 patients when the hGH therapy was discontinued. The causes for this improvement in growth are possibly multifactorial: the growth rate is depressed by the severity of the disease and high-dose glucocorticoid therapy. Increases of growth rate occurred during improvements in the disease, reduction of steroid medication, as a result of therapy with human growth hormone, and because of puberty in some patients. Human growth hormone seemed to improve the underlying condition of four of the patients but had no influence on the disease in the remaining children.