It is known that some plants can serve as indicators of environmental factors, including the noxious ones. The current knowledge gained in botany and ecology has established that classification of species in different environmental categories is based on complex research of flora and soil. Herbaceous plant species, being quantitatively lower rank layer than trees, are very significant for stationary factors (anthropic and natural factors). It is important to remember that most forest herbaceous plant species are managed as medicinal species and as food for animals, which require quantitative estimation of mineral elements in their composition. Our research was targeted toward evaluation of the relationship between Ca and Mg content in herbaceous plants and soil in seasonal dynamics; tentatively to determine the ecological group of plants with preferences to degree of saturation of soil with bases. Most studied plants are known in the literature as mesothrophic and eutrophic species (Asarum europaeum, Dentaria bulbifera, Euphorbia amigdaloides, Isopirum thalectroides, Galium odoratum, Mercurialis perennis, Dactylis glomerata etc.) and fewer eurimesotrophic (Campanula ranunculoides, Melica uniflora). Magnesium and calcium content was quantitatively determined in the aforementioned plant species. The investigations were conducted on three European-forest ecosystems, experimental plots demarcated territorial area of 1800 m2: common oak with hornbeam forest on typical gray clay forest soils over clay-sandy loam (A); sessile oak with linden and ash forest on brown clay soils over deeply gleyed clay (B); beech with sessile oak forest on brown sandy loam soil over clay-sand (C). The samples were taken from each of eight allotted 1 m2 areas in each type of forest. Calcium. The calcium content (average values) in plants varied from 0.48 up to 0.7% (the min. 0.3%, max. 1.9%) for species Carex brevicollis L. and Carex pilosa L. Scop., up to 3.6% for Mercurialis perennis L. (min. 1.1, max. 3.8%) and 4.0% for Lunaria redeviva L. (3.8 to 4.2%). Although Ca2 + was found at comparative lower levels in brown sandy loam soil over clay-sand (C), average –  in gray clay forest soils over clay-sandy loam (A) and large – in brown clay soils over deeply gleyed clay (B), the last two being with enormous accumulations of Ca2 + in some areas, plants showed variations in small intervals. In an interval with values of Ca2+ less than 1% common species such as Carex pilosa Scop. and Carex brevicollis L. (for A, B, C forests) were included. Hordelymus europaeus (forest B) and Melica uniflora Retz. (Forest A, B) were also included in the 1% interval. Most studied species were within 1 - 2%. Species Alliaria petiolata (Bieb.) Cavara et Grande (forest B), Gallium odoratum (L.) Scop. (forests A,B,C), Lamium maculatum L., Syphytum tauricum Willd. (forest B) were framed within the limits of 2-3%. Just for the species Mercurialis perennis L. (ABC) and Lunaria redeviva L. (forest B) the amount of Ca2 + was in the range of 3-4%. Magnesium. Magnesium is at the boundary between macro and micronutrients. Mg content in the investigated plants varied mostly within 0-1%, most plants having less than 0.5%. Species Campanula rapunculoides L.(forest A), Carex brevicolis L., Carex pilosa Scop.(A,B,C) were all characterized by values less than 0.3%. Species Asarum europaeum L. (forests A,C), Dentaria bulbifera L. (forests A,B,C), Euforbia amigdaloides L. (forests A,B), Mercurialis perennis L. (forests A, B, C) and Viola hirta L. (forests A,B) contained values greater than 0.5%. The studied soils were characterized by a high degree of base saturation. Most plants were known as eutrophic, mesothrophic, some megatrophic and eurimesotrophic. However, quantitative ratios of Ca and Mg in the soil comparing with the ones in the plants, at the moment, cannot express veridical interdependencies. Authors are thankful to "Soros" Foundation (Research Support Scheme no. 245/2000) for their financial support in carrying out this research project.