to investigate the difference in serum tryptase levels between post-acute COVID-19 syndrome (PACS) patients and controls.PACS has been defined as symptoms that persist for more than 3 months after the onset of COVID-19. The pathogenesis is still unknown, but mast cell activation has been proposed as one of the mechanisms, and increased serum tryptase levels have been demonstrated in PACS patients.A total number of 133 patients were included: 50 with PACS, 37 asymptomatic COVID-19 convalescents, and 46 controls with a negative history of COVID-19. Serum tryptase levels were determined in all participants.There was no significant difference in serum levels of tryptase among the groups.the role of mast cell activation in PACS remains unclear and further research is needed to fill the gaps in understanding the pathogenesis of this complex and heterogeneous disorder (Tab. 2, Ref. 17). Text in PDF www.elis.sk Keywords: post Acute COVID-19 syndrome, tryptase, mast cells, lactate dehydrogenase, ferritin.