The synthesis of a number of 3,4-dihydrospiro-2H-1,3-benzoxazines and their corresponding benzoxazinium salts are reported. The saluretic effects displayed by these N,O-spiroannulated 2-(aminomethyl)phenols appear to be, in part, inversely related to their respective in vivo rates of hydrolysis. Good antihypertensive effects are found only in spirobenzoxazinium 22. Thus, a combination of spiroannulation and quaternization on 2 to produce 22 leads to a loss of saluretic effects with maintenance of antihypertensive effects and, thereby, serves to separate these pharmacological properties.