Medicinal plants form an organic compartment of the natural wealth of each state. Middle and Eastern Europe, particularly provenience of Slovakia, possesses giant opulence of flora. Good vegetation conditions have influenced and influence also the formation of components in our medicinal plants. In the past, these were harvested by individual collection. At present, having well developed pharmaceutical industry, this form of growing and collection is not sufficient and the medicinal plants require a planned way of growing. Melissa officinalis belongs to the plants of great significance and pharmaceutical use. From that point of view it was important to determine, which conditions and to what extent are optimum for the plant growth, and at which conditions is the essential oil content highest and qualitatively most advantageous.

In our work, the content and relative abundance of main components of the essential oil from Melissa officinalis during its whole vegetation period were studied. It has been shown, that amount of the essential oil increase before flowering till the very start of flowering, when it reaches the maximum level. At gradual aging, on the other hand, the essential oil content decreases till biological ripe. The content of main components is changing in dependence on the position of leaf insertions. The percentage of the most important constituents, i.e. neral and geranial, gradually decreases from the growth tops to the bottom leaf insertions, while the percent of another important substance citronellal has been changing acropetally.