The effect of acids and bases on the solubility of amino acids at 298.2 K, within the pH range, (pH from 2 to 10) and out of the pH range, was determined. The amino acids considered were glycine, DL-alanine, DL-valine and DL-serine. The acids used were HCl and HNO3 and the bases NaOH and KOH. It was observed that in the pH range (pH from 2 to 10) there is no significant difference in the solubility of DL-alanine in the presence of different ions such as Na+ or K+ at high pH, and Cl- or NO3- at low pH values. However, at higher concentrations of the acids or the bases, there is an effect of the counterions in solubilities. For all the amino acids considered here the solubility was higher in nitric acid, as compared to hydrochloric acid, and higher in potassium hydroxide than in sodium hydroxide. (C) 1998 Elsevier Science B.V. All rights reserved.