New, natural products, hierridin B and hierridin A, have been isolated from the lipophilic extract of the marine cyanobacterium _Phormidium ectocarpi_. The isolated hierridin mixture showed antiplasmodial activity towards _Plasmodium falciparum_[13]. The specific antictumour activity of two _Phormidium molle_ strains was reported by [PERSON] et al., studying their in vitro cytotoxic and anticancer properties on five cancer (HeLa, Jurkat, U-937, A2058, and RD) and two normal (3T3 and FL) cell lines [6]. Treatment with _Phormidium_ extracts or _Phormidium_ growth media altered the cytoskeletons and microtubule network of adherent cells, causing dose-dependent destruction of the monolayer and morphological changes. An extract concentration of 10 \(\mathrm{\mu}\mathrm{g}\)/mL showed significant cytotoxicity on HeLa and A2058 cells 24 h after treatment (41% and 60% respectively) as determined with MTT assay, while the viability of other cells was not significantly affected [6]. Portoamides A and B are cyclic peptides isolated from the cyanobacterium _Phormidium_ sp. LEGE 05292 and were shown to be cytotoxic against RPE-1 (normal epithelial) and HCT116 (colon carcinoma) cell lines [14]. The problem is that many of the isolated bioactive cyanobacterial compounds have complicated chemical structures that will be difficult to synthesize. On the other hand, to purify a certain compound, a huge amount of cyanobacterial mass is required. Thus, before starting with purification or chemical synthesis of the desired compound, it is necessary to know the exact mechanism of its action. To speed the process of discovery of new bioactive compounds from cyanobacteria, [PERSON] et al. developed an automated library of cyanobacterial fractions in a format of 96-well mother plates that can be easily screened with different bioassays and even coupled with metabolomics analysis [2]. Currently, only 10-20% of the known cyanobacterial secondary metabolites are characterized in terms of their chemical structure and biological potential [15; 16; 17]. Most common are the lipopeptides (40.2%), amides (9.4%), amino acids (5.6%), macrolides (4.2%), and fatty acids (4.2%) [4]. On the other hand, the variability of chemical structures produced by cyanobacteria allows interaction with different cellular targets, leading to hypotheses about new mechanisms of cyanobacterial action [18; 19]. In this study, we suggest a novel approach for assessing the immunomodulatory properties of natural products derived from cyanobacteria. By using three staining panels (for T cells, antigen-presenting cells, and NK cells) and human peripheral blood mononuclear cells (PBMCs) from healthy individuals, the status of the main immunocompetent cells treated with natural products can be easily determined by flow cytometry. In addition, the observed effects can be related to certain compound(s) determined by mass spectrometry within the tested natural product. Thus,the aim of our study was to evaluate the immunomodulatory properties of cyanobacterial extract from _Phormidium papyraceum_ Gomont ex Gomont 1892 (strain PACC 8600) and to determine its chemical composition. The proposed bioactive compounds could be additionally isolated and assessed (when this is possible). Here, we also evaluated the antibacterial activity of the studied cyanobacterial extract.