A total of 21 patients with somatotropic deficiency have been enrolled in a clinical trial of biosynthetic growth hormone (bio-GH) and pituitary growth hormone (pit-GH). Five of them not previously treated (naïve) and 7 previously treated with pit-GH, received bio-GH; 9 received only pit-GH. Biosynthetic-GH was given 12 UI/m2/week. Height velocities during treatment rose, for naïve patients, from 3.6 +/- 0.3 cm/year (before treatment) to 8.7 +/- 1.3 cm/year (after 12 months treatment). For previously treated patients, after a period at least 6 months without any GH therapy, the increase in height was from 2.5 +/- 0.9 cm/year to 6.8 cm/year; and for the patients who received only pit-GH was from 3.4 +/- 1.2 cm/year to 8.0 +/- 1.1 cm/year. No significant difference was observed between the growth velocities obtained with the two preparations. No specific side-effects were noted.