Cytokine signalling plays an important role in controlling many aspects of our bodies from embryo development to coordinating immune responses against pathogens. Granulocyte colony stimulating factor (GCSF) is a cytokine that stimulates the production of neutrophils in the bone marrow. Recombinant GCSF is frequently used in the clinic to boost the neutrophil count of cancer patients suffering from chemotherapy-induced neutropenia. Conversely, as a pro-inflammatory cytokine, activation of GCSF signalling has been implicated in inflammatory disorders such as rheumatoid arthritis. GCSF signals via the GCSF receptor (GCSFR), a homodimeric type I cytokine receptor and member of the tall cytokine receptor family. This family is characterised by an N-terminal Ig-like domain and three C-Terminal Fn(III) domains flanking a cytokine receptor homology domain (CRH). At present, the only high-resolution structures of the GCSF-GCSFR signalling complex lack the Fn(III) leg domains. These missing domains are critical for signal transduction so if we are to properly understand the mechanism of receptor activation and signal transduction across the membrane following ligand binding, this information is required. We have generated sufficient quantities of recombinant GCSF and GCSFR ectodomain to enable structural and biochemical studies. We have characterised the complex by SECMALS and are using cryo-electron microscopy to obtain a structure of the full ectodomain in complex with cytokine.