This chapter describes the simple substituted quinazolin-4-ones, the pyrroloquinazolines, the pyrido[2,1-b]quinazolines, the indoloquinazolines, biosynthesis, and biological activity of quinazoline alkaloids and their analogs. Febrifugine is perhaps one of the most interesting quinazoline alkaloids. Both glomerin and homoglomerin have been isolated as crystalline components from the defensive secretion of the glomerid millipede Glorneris marginatu.1H-NMR spectra of both alkaloids show the presence of four aromatic protons. The new alkaloids vasicoline, vasicolinone, and adhatodine and anisotine are found only in young plants of Adhatoda vasica in very low yield. The isolation of pure vasicoline and adhatodine is difficult, because both bases are oxidized to vasicolinone and anisotine by atmospheric oxygen. Anthranilic acid (N-methylated where necessary), ammonia or amine, and formic acid or phenylacetic acid derived from phenylalanine units or their equivalents build up the simple substituted quinazoline derivatives. Vasicine is reported to be a bronchodilator, a respiratory stimulant, and hypotensive in action. Its activity against histamine-induced bronchospasm is specific but brief. © 1986, Academic Press, Inc. All rights reserved.