S100B is a neurotrophic protein detectable in biological fluids and in human milk. Since there are several maternal-neonatal conditions requiring the administration of animal milks the aim of the present study was to quantify S100B in milk from different mammalian species and to compare protein's concentration among human and mammalian milks. We assessed S100B concentrations in donkey (n=12), goat (n=15) sheep (n=15), commercially available cow (n=8) and human (n=15) milk samples. S100B measurements were performed using an immunoluminometric assay. S100B concentration in human milk (10.41 +/- 4.2 microg/L) was higher (P LESS THAN0.001) than mammalian milks. Of note, S100B concentration in cow milk (3.13 +/- 0.56 microg/L) was higher (P LESS THAN0.01) than that showed in donkey (1.17 +/- 0.26 microg/L), sheep (0.25 +/- 0.11 microg/L) and goat (0.26 +/- 0.11 microg/L). S100B in donkey milk was higher (P LESS THAN0.01) than sheep and goat samples whilst protein's concentration did not differ between goat and sheep. The present study suggests the opportunity of S100B addition to animal milk intended for infant feeding.