In 44 girls with Turner's syndrome, aged 4.0-15.3 yr, the effects of biosynthetic GH (25 U/m2.week) given as once daily or twice daily injections were compared. During 1 yr of treatment, the growth rate increased similarly by 3.5 +/- 1.3 cm/yr in the once daily group and 2.7 +/- 1.8 cm/yr in the twice daily group. Although pretreatment height velocity was negatively related to age, the increase in height velocity during therapy was not. The mean progression in bone age (TW2-RUS method), during therapy was 1.3 yr in both groups. No significant change in the median insulin secretory response to an oral glucose tolerance test was found. Serum cholesterol and triglyceride concentrations did not change significantly throughout the study in either treatment group. Thyroid hormone concentrations remained within normal limits. Normal increments in left ventricular wall thickness and left ventricular mass for age and body surface were observed after 1 yr of GH treatment. We conclude that division of the daily GH dose given to Turner's syndrome patients into two injections does not result in either a significantly different growth response or different side-effects from once daily treatment during the first year of therapy.