The entire cDNA sequence of the growth hormone receptor (GHR) of the Chilean flounder (Paralichthys. adspersus) was cloned by RT-PCR and RNA ligase rapid amplification of 5' and 3'ends. The deduced amino acid sequence contains 641 residues and codes for the GHR1 form. The receptor includes all the structural domains and motifs responsible for its interaction with the growth hormone and growth signal transduction. Sequence comparison revealed 95 and 88% identity with other flat fish such as the Japanese flounder and Atlantic halibut respectively, but decreased to 41% with the GHR of other teleosts such as salmon. In addition we performed a phylogenetic analysis of this receptor in teleosts. RT-PCR experiments were performed to study the expression of GHR1 mRNA in different tissues of juvenile fish, detecting the transcripts in all tissues investigated with higher expressions in the liver, brain and gonads. Additionally, using whole-mount in situ hybridization in larvae stages, we observed an on and off GHR1 mRNA expression pattern. This novel finding evidences that during early development of a teleost, GHR1 is transiently expressed in somites, a source of muscle, bone and spinal chord precursors cells, suggesting a relevant role of GH in fish development. GHR1 was also temporally detected in the notochord, intestines, brain and retinal layers, before its ubiquitous establishment.