Tryptase is used as a marker in many clinical conditions such as mast cell activation and systemic anaphylaxis. Normal levels of the serum basal tryptase (sBT) are determined in adulthood; however, data about nonallergic healthy children is limited. This study was designed to determine the normal sBT levels in healthy children. Total sBT levels were measured in 113 sera from healthy nonallergic children, for routine follow-up or diagnosis of illnesses that are not known. to induce changes in serum tryptase levels. One hundred thirteen children aged 0.16-9.91 years (male/female subjects, 68/45 [60%/40%]) with a median (interquartile) age of 3.36 years (1.94-5.68 years) were evaluated. The sBT level was determined to be 3.30 ng/mL (2.38-4.36) median (interquartile) for the whole group. There was a tendency of higher sBT levels for boys than girls (3.49 [2.56-4.64 ng/mL] and 2.91 ng/mL [2.16-4.16 ng/mL], respectively); however, these, findings were not significant (p = 0.12). The analysis of the whole group revealed that sBT levels were inversely related with age (r = -0.259; p = 0.006); and the decrease of sBT with age was more prominent in girls (r = -0.282; p = 0.02) than in boys. The highest sBT levels were found in the 0- to 1-year age group (all, 4.67 ng/mL [4.04-6.39 ng/mL]; boys, 5.34 ng/mL [4.04-6.39 ng/mL]; girls, 4.48 ng/mL [3.23-16.26 ng/mL]). The sBT levels in healthy children are similar to those in adults except in infancy. Interestingly, sBT levels tend to decrease slightly with age. Although they,did not reach significance, sBT levels were found to be higher in boys compared with the girls.