GSL I-B4 isolectin contains only the B subunits. It is a useful marker for endothelial cells from nonprimates such as mouse, rat, rabbit, and goat as well as a marker for non-peptidergic unmyelinated primary afferent neurons. This “B”-rich lectin preferentially agglutinates blood group B cells and is specific for α-galactose residues. Fluorescein labeled GSL I-B4 has an appropriate number of fluorechromes bound to provide the optimum staining characteristics for this lectin. This conjugate is supplied essentially free of unconjugated fluorescein and is preserved with sodium azide. Excitation maximum = 495 nm; emission maximum = 515 nm. Color = green.