Анотация: This paper presents research on the concentration of microcystins produced by Microcystis aeruginosa (Kutzing, UTEX 2667). The relationship between the production of microcystins, the algae growth and the content of chlorophyll a was investigated at five temperatures (range 20-38C) and two light intensities - 8000 lx and 2x8000 lx. ELISA method was used for measuring the toxin level. Optimal conditions for the production of microcystins at 25-26C were observed. Neither of the two light intensities impacted the amount of microcystins. HPLC-DAD quality analysis for determination of microcystins in the algal biomass was performed. The results showed presence of microcystin-LR and six unknown peaks possessing characteristic microcystin-like UV-spectra, which are of interest for future investigations