This paper presents the results of research on the antibiotic sensitivity of bacteria inhabiting the surface microlayer (SM) and the subsurface water (SSW) of Lake Jeziorak Mały. It follows from the results that doxycycline, oxytetracycline and nalidixic acid are characterized by the strongest antibacterial effect. For some antibiotics, different strengths of the effect on bacteria isolated from the surface microlayer and subsurface water have been observed.