BioLegend's FOXP3 Fix/Perm Buffer Set has been specially formulated for intracellular staining FOXP3 with minimum effect on the surface fluorochrome staining. It contains one 30 ml 4X concentrated FOXP3 Fix/Perm buffer (Cat. No. 421401) and one 25 ml 10X concentrated FOXP3 Perm buffer (Cat. No. 421402). The FOXP3 Fix/Perm buffer(4X) must be freshly diluted to 1X working solution with PBS (10 mM sodium phosphate, 150 mM sodium chloride, pH 7.2) prior to staining procedures. e.g. Dilute one (1) part FOXP3 Fix/Perm buffer(4X) to three (3) parts PBS. The FOXP3 Perm buffer (10X) should be diluted to 1X working solution with PBS (10 mM sodium phosphate, 150 mM sodium chloride, pH 7.2) prior to staining procedures. e.g. Dilute one (1) part FOXP3 Perm buffer(10X) to nine (9) parts PBS.Caution: The FOXP3 Fix/Perm buffer contains paraformaldehyde, which is toxigenic and mutagenic. Please handle with caution and wear gloves, lab coat and necessary protection to avoid direct body contact.