The growth hormone receptor (GHR) mediates growth hormone (GH) effects by activating the GHR-associated cytoplasmic tyrosine kinase, JAK2. Recent studies indicate that GHRs exist as dimers independently of GH binding. Some authors suggest that receptor predimerization is mediated by the transmembrane domain (TMD) and that GH binding initiates signaling by triggering changes in the orientation of the two GHRs within the dimer. In this study, we investigate the role of GHR TMD in GH-independent receptor dimerization and ligand-induced activation. We prepared a GHR mutant, GHRLDLR, in which the TMD is replaced with the TMD of the human low density lipoprotein receptor (LDLR). The resultant chimera has a TMD two residues shorter than the native GHR TMD; thus, in addition to possessing a different TMD, the altered GHRLDLR TMD helical register may change positions of the GHR extracellular (ECD) and intracellular (ICD) domains relative to the TMD when compared to the wild-type (WT) receptor. When each was coexpressed with an ICD-truncated GHR mutant, GHR1274-Myc, both WT GHR and GHRLDLR were specifically coprecipitated with GHR1-274-Myc, indicating that the GHR TMD was not required for GHR heterodimerization with GHR1274-Myc. We further examined the contribution of the so-called "dimerization interface", a GHR ECD region which is critical for GH-induced signaling, to receptor predimerization. Coimmunoprecipitation experiments with either WT GHR, a "dimerization interface" mutant (GHR-H150D), or a control mutant (GHR-T147D) with GHR1-274-Myc showed dramatically reduced coprecipitation of GHR-H150D with GHR1274-Myc when compared with WT GHR or GHR-T147K. This result suggests that, in contrast to some recent models, the "dimerization interface" contributes to GHR predimerization. We also compared WT GHR with GHRLDLR and GHRLDLRF4 (a chimera in which the LDLR TMD has an internal deletion of 4 residues) with regard to response to GH stimulation. Although the chimeras had similar GH dose responses and time courses for signaling as WT GHR, they were markedly less sensitive to inhibition of signaling by a conformation-sensitive GHR ECD monoclonal antibody. Further, the chimeras were much less sensitive to inducible metalloprotease cleavage than was WT GHR, implying that the ECD conformations of the chimera receptors differ from WTGHR. Collectively, our data indicate that the composition and/or length of the TMD affect some aspects of GHR function, but do not affect receptor predimerization or GH-induced GHR activation. Further, they suggest that the GHR ECD-TMD is more flexible than previously thought in terms of the ability to achieve the active conformation in response to GH.