Marine toxins are produced by certain toxic phytoplankton species. Harmful toxins may accumulate in the shellfish tissue, potentially impacting human health. Paralytic shellfish poisoning (PSP) is a syndrome caused by ingestion of shellfish contaminated with paralytic shellfish toxins (PST) that comprise saxitoxin and its variants (neosaxitoxin, gonyautoxins and their decarbamoyl and N-sulfocambamoyl analogs). The aim of this study was to evaluate the presence of paralytic shellfish toxins (PSTs) in plankton samples and in mussels intended for human consumption. Mussels collected in the main areas of production and recreational harvesting off the north coast of Bulgaria have been investigated for PSP toxins. Individual toxins were determined using two methods both involving fluorescence detection: ion pair-liquid chromatography with post-column derivatization (method 1) and high-performance liquid chromatographic procedure employing pre-column oxidation of the toxins (method 2). The results according method 1 demonstrated the presence of gonyautoxin 2 in 53% of the mussel samples and no toxins were detected in the plankton samples. The toxicity level - 1.6 μg STX.2HCl .kg-1 was far beneath the EU legislative limit of 800 μg STX.2HCl .kg-1 concluding in negligible risk for human health. Due to higher limits of detection no toxins were detected via method 2. Even though, considering method 2 is recognized by European Commission as official for regulatory purposes and the relative high value of the legislative threshold, thus obtained toxin levels are enough representative to conclude if mussels are safe for consumption or not. On the other hand, the more sensitive method 1 provides important data on extremely low toxin levels which would be useful for chronic exposure estimation and for completing the knowledge about occurrence of PSTs in certain locations.