0.5M Histidine Hydrochloride, pH 5.5 is a solution of histidine hydrochloride in purified water at 0.5 M, adjusted to pH 5.5. It is supplied as a concentrate for dilution to working-strength histidine buffers. The 1 L fill supports laboratory and pilot-scale buffer preparation.

It is commonly used as a stock for preparing histidine buffers for biologic formulation development. Diluting 1:50 gives 10 mM histidine and 1:20 gives 25 mM, the range typical of monoclonal antibody formulation buffers. Verify pH after dilution and after adding sugars or surfactants.