Effects of cysteamine hydrochloride (CSH)-a somatostatin-inhibiting agent-on serum growth hormone (GH) levels and growth in juvenile grass carp (Ctenopharyngodon idellus) were studied. Intraperitoneal (i.p.) injection and single or 10-day feeding of different doses of CSH significantly increased serum GH levels. CSH and luteinizing hormonereleasing hormone analog (LHRH-A, D-Ala6,Pro9-Net-LHRH), alone and in combination i.p. injection, and single or 10-day administration in diet resulted in an enhancement of serum GH contents; in addition, there was an additive, not synergistic effect of CSH and LHRH-A on elevation of serum GH levels. Ten day feeding of CSH, or CSH and LHRHA, alone and in combination caused a significant increase in muscle RNAyDNA ratio. These results provide evidence that CSH significantly increases serum GH levels and promotes short-term growth in juvenile grass carp.