Studies on cytokinin-like substances synthesized by planktonic bacteria isolated from littoral and pelagial zones of the lake Jeziorak in spring and summer have been carried out. 62.5% of bacteria isolated in summer, and 12.5% of bacteria isolated in spring were able to produce cytokinin-like substances. Among synthesized substances there occurred isopentenyladenine (2iP, i⁶Ade), zeatin (Z, io⁶Ade) and zeatin riboside (ZR, io⁶A). No trace of isopentenyladenosine (2iPA, i⁶A) was detected. The amounts of cytokinin-like substances produced converted into 1 g dry mass of bacteria were as follows: 9.97 - 21.59 mg for isopentenyladenine; 3.08 - 35.08 mg for zeatin, and 0.35 - 18.69 mg for zeatin riboside. Various taxonomic group of bacteria were capable of synthesising those compounds, such as Vibrio, Bacillus, Aeromonas, Achromobacter genera and Enterobacteriaceae family. Among the analysed bacteria it was only the strain of Achromobacter spp that produced two compounds at the same time (zeatin and zeatin riboside).