A fluorescent label compound of formula ##STR00001## where Z is a reactive group that can be used for covalent coupling of the fluorescent label compound to other molecule. Either the fluorophore is a dipyrrometheneboron difluoride dye and Y is a water-solubilizing moiety, or Y is --CH.sub.2CH.sub.2SO.sub.3.sup.- X.sup.+ where X.sup.+ is a cation. The use of the compounds in bianalytical assays and cytological or histological staining methods, and a method for increasing the hydrophilicity of fluorescent compounds, are also disclosed.