In each one of the samples, investigation of osmolarity, concentration of sodium chloride and proteins and bacteria was carried out. With these data, concentration of solutes in milks was estimated, together with a calculation of renal charge they represented. The most outstanding results showed that mothers offer whole and half skimmed milks at concentrations less than normal dilutions; thus, the solute charge was found in most cases, far below figures reported as average. In a good number of milks, osmolarity showed to very high, specially in those added with corn syrup. Only in 9 of the formulas germs were not identified; in the rest, E. coli predominated and there was high index of contamination.