The properties of a new fluorescent retrograde neuronal tracer, green fluorescent latex microspheres ("beads"), are described. Green beads, like the red beads that have been in use for several years, are readily transported by neurons in the mammalian central nervous system. After survival times ranging from 24 h to over one month they produce a distinct granular green fluorescence in the neuronal cytoplasm that is highly resistant to fading, when viewed using fluorescein filter sets. Green and red beads are transported with similar efficacy; cells labelled with either one or both tracers are easily distinguished. When injected into the brain, green beads, like red beads, show only minimal diffusion from the injection site. Because these two tracers differ only in their fluorescence, they should be ideal for double-labelling studies in a wide variety of systems and in developmental studies in which long-term retention of labels is required.