To test whether RI-3 affects agonist-induced FPR1 activation, rat basophilic leukaemia RBL-2H3 cells devoid of FPR1, and RBL-2H3/ETFR cells stably expressing FPR1, were pre-incubated with diluents (None), an excess of fMLF, RERF, ERFR, or RI-3 for 60 min at 4 °C (to avoid FPR1 internalization), and then exposed to 10 nM N-formyl-Nle-Leu-Phe-Nle-Tyr-Lys-fluorescein (FITC-fMLF) for additional 60 min at 4 °C. This evidence concerns the gene FPR1 and acute basophilic leukemia.