###### Abstract  
Freeze-dried stems and caps of six cultivated mushroom species, namely _Agaricus bisporus_ (white) _Agaricus bisporus_ (brown), _Lentiula edodes_, _Pholiota namoko_, _Pleurotus eryngi_i_ and _Pleurotus ostreatus_ were subjected to ethanolic extraction. The obtained extracts were analyzed in terms of total phenolics content, total flavonoids content and antioxidant capacity, and the results were calculated per gram of mushroom dry weight and extract dry weight. The LC-MS technique was applied to determine the profiles of phenolic acids. The amount of total phenolics in the stems (per the fruiting bodies' dry weight) ranged from 1.09 \(\pm\) 0.09 mg/g (_P. ostreatus_) to 4.02 \(\pm\) 0.20 mg/g (the white _A. bisporus_), whereas in the caps it ranged from 1.49 \(\pm\) 0.07 mg/g (_P. namoko_) to 6.22 \(\pm\) 0.21 mg/g (the brown _A. bisporus_). The total flavonoid content in the stems (per the fruiting bodies' dry weight) varied from 0.46 \(\pm\) 0.05 mg/g (_P. ostreatus_) to 1.72 \(\pm\) 0.02 mg/g (the brown _A. bisporus_), and in the caps it ranged from 0.48 \(\pm\) 0.01 mg/g (_P. ostreatus_) to 1.93 \(\pm\) 0.05 mg/g (the white _A. bisporus_). The antioxidant potential measured with the FRAP assay showed that the caps displayed higher activity compared to the stems. However, in the case of the DPPH assay performed on _A. bisporus_, this relationship was inverted. Different species contained varied concentrations of phenolic acids. _P. eryngi_ caps contained the highest amount of 3,4-DHBA, _L. edodes_ caps were the richest source of caffe acid, whereas the highest amount of syringic acid was observed in _L. edodes_ stems. The caps of _P. namoko_ contained the highest amounts of _p_-coumaric and t-cinamamic acid, as well as 4-hydroxybenzaldehyde. health-promoting properties. Mushroom-based products such as dietary supplements, nutraceuticaluls and medicines have appeared on the market [4]. The health-promoting potential of fungi is related to their various activities, including immunomodulating, cardioprotective, antimicrobial, antiviral, antioxidant and antitumor behaviors [5]. Compounds such as high-molecular polysaccharides, terpen and proteins are primarily responsible for the antitumor effect. Cardioprotective effects are attributed to compounds such as polysaccharides, or low-molecular weight compounds which decrease the content of cholesterol in the blood (lovastatin, erythadenine) [6]. The antioxidant effect of mushroom fruiting bodies is mainly caused by the presence of phenolic compounds and, to a lesser extent, by vitamins, sterols or unpurified polysaccharides [7]. Polysaccharides, terpen, phenolic acids and proteins were reported to exert antiviral properties [8], while antimicrobial effects were attributed mainly to oxal acid, benzoic acid, peptides and terpenes [9]. Dietary supplements and nutraceuticaluls based on mushrooms often have a form of concentrated extract, either aqueous or alcoholic, with varying degrees of purification. These extracts can be in the form of solutions but also can be dried, and sold as powders or tablets [4]. The raw materials used for their production are primarily the fruiting bodies of cultivated edible or inedible mushrooms (sometimes referred to as medical). In order to reduce the cost of the production of mushroom extracts, manufacturers try to use inferior raw materials (too-small or too-large fruiting bodies, or fruiting bodies with fully-open caps), as well as production waste such as stems [10]. It is worth noting that the content of individual bioactive components in mushrooms varies depending on the morphological parts of the fruiting body. So far, this has been the subject of several studies. Some authors reported a higher content of total phenolic compounds and antioxidant capacity in mushroom caps [11; 12]. Similarly, other authors reported substantially higher content of protein in caps than in stems [13]. On the other hand, in the case of high-molecular-weight polysaccharides, this relationship may be reversed [14].