Nile blue, introduced by Lorrain Smith for distinguishing between neutral fats (triglycerides) and fatty acids, was considered by Lison to be of no histochemical value except that the red coloration was specific for lipoids in general. This conclusion was based principally on Lison's own researches, and in part on those of Kaufmann and Lehmann.
Reinvestigation has shown that some of Kaufmann and Lehmann's results are of doubtful value and all require careful interpretation, but in general these and other results lead to the conclusion that nile blue can be used to distinguish neutral lipoids (esters and hydrocarbons) from acidic lipoids (phospholipines and acids). Cholesterol is not detected. A method for using both the oxazine and oxazone of nile blue is described, which has greater sensitivity to acidic lipoids.