In the course of some studies on chemical control of pests of legume crops it has become desirable to mark honey bees at the hive and, if possible, at the flower. Considerable success has been achieved by the use of the compound fluorescein. It has been found that bees can be dusted with small quantities of fluorescein and that the presence of the material can subsequently be detected by means of a Coleman photofluorometer and by eye. It seems likely that quantitative measurements could be made with a photofluorometer.