The complexation constants of neutral and protonated procaine (also called novocaine) with beta-cyclodextrin have been obtained as a function of sodium chloride concentration, at 25 degrees C, using the potentiometric technique with a glass electrode. It was found that the formation of the complex with protonated procaine is not altered by the presence of the salt and the logarithm of the formation constant of the neutral complex increases slowly with ionic strength, varing linearly with salt concentration.