Nitrogen-containing and other secondary plant products have evolved as a consequence of the struggle between the plant and the animal kingdoms, the latter directly or indirectly thriving on plants. During evolution plants developed bioactive and exceedingly complicated chemical structures that serve the purpose of plant defense. It is this property of those plants that has been exploited by mankind as medicines, poisons and recreational drugs. Three classes of nitrogen-containing plant products are being reviewed in this article: the alkaloids, the cyanogenic glucosides/glucosinolates and the nonprotein amino acids. It is the interplay of different scientific disciplines such as chemistry, pharmacognosy, medicine, analytics, cell biology, molecular biology, botany and chemotaxonomy that form a new and exciting area called "phytochemistry". It is foreseeable that this integration of disciplines across traditional borders will bring new achievements in phytochemistry, as history has taught us already.