Background: Mast cells are dispersed in many tissues, especially in digestive and respiratory-tract mucosal membranes. Tryptase, considered a marker of mast-cell activity, is the most important protease released from these cells during degranulation. Tryptase concentration is mainly accessed in anaphylaxis and mastocytosis, being one diagnostic criteria of this disease. There are no data concerning tryptase activity in healthy children in the current literature. Aim: The aims of this study were the analysis of concentrations of serum tryptase in healthy children, and determining reference values of the enzyme at different developmental ages. Materials and methods: The investigated group consisted of 131 healthy children (75 girls, 56 boys) aged 3 months-18 years. The concentration of tryptase in the studied samples was evaluated by the fluoro-immuno-enzymatic method with UniCAP. Results: The mean concentration of serum tryptase in the studied group was 2.8±2.2 ng/dL: 2.5±2.2 ng/dL in girls and 3.2±2.1 ng/dL in boys. Conclusion: The upper reference limit of 7.2 ng/dL was lower than in adults.