Introduction Aloe has been used by people as medicinal plants for long time . The main active substance in the fresh juice of aloe is aloin , which contains the sum of anthraquinones ( izobarbaloin , barboloin , emodin ) . The presence of these anthraquinones causes the effects of aloe juice as  nutrient stimulant , antiinfl ammatory , antibacterial agent , stimulant of tissue regeneration , immune stimulant and antimutagenic activity . The aim of our study was to determine whether aloe retain their biological active substances in the greenhouse conditions. Material and methods The aloe greenhouse  collection  of the Botanical Garden of   Republic of  Moldova has 50 species and varieties. We have selected seven species which are used according to the literature as pharmaceuticals . This Aloe arborescens Mill., Aloe barbadensis Mill., Aloe eru Berger., Aloe ferox Mill., Aloe plicatilis Mill., Aloe saponaria Haw., Aloe succotrina Lam. As an indicator of the biological activity of aloe juice was taken aloe anthraquinone - emodin as most easily determined in the laboratory conditions. To determine the aloe -emodin in the juice  of test plants we used technique  of Gaikwad and  Sucheta (1). Namely, linkage of aloe leaf in an amount of 10 g was milled and mixed  with 100ml of 70%  ethanol. Samples we placed   for  extraction within 7 days at room temperature . The presence and amount of free emodin in aloe juice    was determined by SF- 42 spectrophotometer at a wavelength of 437nm and  pH= 6,8  Total emodin in  juice (which includes both free and chemically bound forms) was measured   adjusting  the pH to 10.8 using a solution of NaOH at  wavelength of 529nm . Results and discussions These studies produced the following results. All species contain in the juice biologically active substances in the form of anthraquinone aloe-emodin . In a free state most aloe -emodin was found in the juice of Aloe plicatilis (32,5 units.), Aloe barbadensis (22,5 units ) and Aloe arborescens (  20 units ) Free emodin  in the juice of Aloe succotrina  was the lowest of all studied species (11 units ) but the total quantity of emodin estimated in  the alkaline  medium in this species was the biggest and  attends 42 units . Conclusion From the foregoing , we  can conclude the following: aloe , even when grown in greenhouses retain their biologically active substances’.