We designed a probe based on the fluorescent tracer formyl-Nle-Leu-Phe-Nle-Tyr-Lys(FITC)-OH (Tracer-FITC, Figure ), which has a reported KD of ~3 nM and has been widely used in flow cytometry assays for FPR1. We prepared Tracer-FITC by solid phase peptide synthesis: the Nterminus was formylated via an optimised procedure using p-nitrophenyl formate and the lysine side chain was protected with an orthogonal protecting group (ivDde) that was removed using 4% hydrazine prior to coupling of the FITC fluorophore. To create a probe and incorporate a crosslinking group with minimal changes to this structure, we replaced the N-terminal norleucine residue with photo-methionine. Probe-TAMRA (Figure ) was prepared via SPPS with the C-terminal fluorescein replaced with 5(6)-TAMRA to enable orthogonal visualisation of the two reagents in assays. A TAMRA version of the tracer has previously been used to visualise FPR internalisation in cells, suggesting that the nature of the fluorophore is not critical to receptor binding. Probe-TAMRA was prepared in an analogous procedure to Tracer-FITC and purified by preparative HPLC in 98% purity and 16% overall yield.