St. John's Wort is a facultative apomictic species known to exist in different ploidy levels. In nature, diploid, tetraploid and hexaploid forms can be found. The most common form is tetraploid. Importance of St. John's Wort as medicinal plants is related to possesion of several pharmaceutical substances, the most important being hypericin and hyperforin. The latter is known as putative antidepressant. While in hypericin can cause phototoxicity, hyperforin not and therefore recent studies of St. John's are predominantly focused on studies of hyperforin content. Hyperforin in the St. John's wort accumulates in translucent glands, which are composed of cavities, the secretory cells and mesophyll-like cells, which are visible to the naked eye. The amount of hyperforin varies considerably among accessions. Therefore, we examined the ploidy of accessions and relations between ploidy, transparent gland size and content of hyperforin. The results show that transparent gland size depends on ploidy, but relation between content of hyperforin and ploidy didn’t give us statistically significant differences. There is a strong positive correlation between the ploidy and transparent gland size (ρ = 0.75), whereas there is a weak correlation between the ploidy and the hyperforin content (ρ = 0.24). The size of transparent gland varies from 9387.7 µm² (hexaploid plant 6/8 BF LP 2006) and 1575.9 µm² (diploid plant 6/4 BF LP 2006). The maximum measured hyperforin content is 18.49 mg/g dry mass (hexaploid plant Stamm 710) and the minimum is 1.30 mg/g dry weight (diploid plant 6/4 BF LP 2006).