DNAs encoding the human histamine H3 receptor have been cloned and characterized. The recombinant protein is capable of forming biologically active histamine H3 receptor protein. The cDNA's have been expressed in recombinant host cells which produce active recombinant protein. The recombinant protein is also purified from the recombinant host cells. In addition, the recombinant host cells are utilized to establish a method for identifying modulators of the receptor activity, and receptor modulators are identified.