This review paper summarizes the current knowledge of enzymes participating in the production of benzylisoquinoline alkaloids. This group of alkaloids comprises, e.g., morphine, codeine, thebaine, and sanginarine, which have an irreplaceable position in pharmaceutical practice. For the time being, chemists have not managed to prepare them synthetically with sufficient efficacy, and therefore the study of the enzymology of their formation remains a topical problem. The paper pays particular attention to the knowledge of individual enzymes on the molecular, or gene level. This very knowledge is essential for possible introduction of molecular-genetic approaches to the cultivation of plants producing therapeutically interesting benzylisoquinoline alkaloids.