A molecule coming from outside an organism can form a ligand-receptor complex. Upon its formation, a message is transmitted, for example, to certain cells. In this way, two enantiomers can emit messages that differ, either quantitatively or qualitatively. In the present article, these facts are taken as a common basis for the actions of chiral drug, pesticide, and fragrance molecules. For each of these groups, a few examples of current interest were selected. At present, the demand for single enantiomers in medicine and agriculture is economically highly significant. We propose a two-hour lecture, emphasizing the similarity between the different types of receptor-mediated actions of enantiomers, thus connecting some seemingly unrelated subjects in the university curricula. The lecture is intended for medicinal chemistry students; in addition, it should be suitable for the third-year chemistry students who are interested in the applications presented here. (Contains 5 tables, 5 figures, and 1 scheme.)