This volume contains the proceedings of the Third International Conference on Insect Neurochemistry and Neurophysiology (ICINN'89), which was held at the University of Maryland at College Park, Maryland, on July 10-12, 1989. The ICINN meetings were ini tiated in 1983 at a time when insect neurobiology was emerging as a vigorous sector of entomology, requiring a degree of attention and autonomy long before granted to its sister field, vertebrate neurobiol ogy. The distinctly medical aspects of the latter were replaced by potentiali ties for developing new approaches to insect control, and the difference was reflected in the kind of sponsorship that has made the ICINNs possible. It is to the credit of the sponsors of the present con ference, i. e., Agricultural Research Service, US Department of Agri culture, American Cyanamid, BASF, Dow Chemical USA, E.I. DuPont de Nemours, Monsanto, Nippon Soda, Rohm and Haas, and Sandoz Crop Protection, that they recognized the need for providing a forum for specialized scientific presentations as well as a medium by which ideas and information could be exchanged directly and cooperation could be planned. As in the previous conferences in 1983 and 1986, the ICINN'89 program contained state-of-the-art plenary lectures or reviews by invited speakers as well as shorter research communications pre sented orally or as posters. The latter two are included here in three sections: neuroanatomy, neurochemistry, and neurophysiology.