It is well known that many steroid compounds, mainly from large stock-raising farms, more frequently end up in rural or communal sewage systems. It is also known that the duckweed family (Lemnaceae), especially Wolffia arrhiza, is more and more commonly used in the biotechnology of purifying the above-mentioned sewage systems due to its heterotrophic and detoxication ability, as well as its ease of adoption to unfavorable environmental conditions. Therefore, our research analyzes the influence of �Ŕ-estradiol and chemically and functionally diversified corticosteroids: cortisone, cortisole (glucocorticoids), 11-deoxycorticosterone (mineralocorticoids) and prednisolone (chemical derivative of hydrocortisone) on chlorophylls and carotenoids content in photoautotrophic Wolffia arrhiza ( ( Lemnaceae Lemnaceae ), growing in municipal Biaystok tap water (rich in minerals but poor in organic components). From the applied steroid hormones in optimal concentration of 10-6M �Ŕ-estradiol caused the strongest stimulatory effect on photosynthetic pigments, a little less strong - cortisone, slight stimulative - cortisole, and weak 11-deoxycorticosterone. Prednisolone showed a weak inhibitory influence on all types of chlorophylls and carotenoids in comparison with the control culture without exogenous hormones. Applied steroid hormones had a weak stimulative influence over chlorophylls a and b in Wolffia; the strongest was �Ŕ-estradiol between the 5th and the 10 th and the 10 th day of cultivation, in the range of 116.5-121.3% in comparison to the day of cultivation, in the range of 116.5-121.3% in comparison to the control value (100%). The researched steroids had a much stronger influence on carotenoid content, especially �Ŕ-carotene, alloxanthin (oxygen - poor xanthophylls) and violaxanthin (oxygen - rich xanthophylls). Under the influence of �Ŕ-estradiol the amount of �Ŕ-carotene rose by the maximum 160.6%, alloxanthin by 187.9% and violaxanthin by 154.3% in comparison to the control. Our research results demonstrated that �Ŕ-estradiol and - from applied corticosteroids - cortisone and hydrocorticosterone, had more stimulatory influence on carotenoid content in Wolffia arrhiza, but less stimulatory effect on unicellular Chlorella vulgaris.