A wide range of latex particles are described which are capable of carrying high concentrations of fluorescent dyes, drugs, and photoactive agents selectively to subpopulations of neurons in vitro and in vivo. Particle size, charge, and concentration were all found to influence uptake into cultured neurons or retrograde transport in vivo. Chromophore loadings of greater than 14% (w/w) were obtained. Incorporation of a photoactivated dye (chlorin e6) into the polymer did not compromise the ability of the dye to produce singlet oxygen following light exposure. We refer to this unique family of latex particles as the latex nanosphere delivery system (LNDS). The LNDS will be usefull for studies of neuroanatomy and nervous system development, as well as more general areas of biomedical research where it is desirable to selectively label subpopulations of cells. The LNDS also offers a means of providing targeted delivery of drugs or photoactive agents to selected subpopulations of cells; this will allow experimentation not currently possible using any existent methodology.