Luminescence and infrared (IR) spectroscopies of pyridine and ammonia adsorption have been used to measure acidities of gamma-alumina. Neither luminescence nor IR spectra of pyridine adsorption show any Bronsted acidity on gamma-alumina pretreated at 400-degrees-C. However, luminescence emission data reveal four weak OH bands even when pretreatment is done at 600-degrees-C. Pyridine and subsequent water adsorption yield six luminescence emission bands. A red shift of the pyridine emission band is found when pretreatment or desorption temperature is increased. IR spectra of ammonia on alumina pretreated at 400-degrees-C show three deformation bands at 1452, 1465, and 1485 cm-1. The first band is also observed together with a band at 1554 cm-1 even for pretreatment at 950-degrees-C, and it corresponds to NH4+ formed from dissociative adsorption of ammonia, while the other two bands are assigned to ammonia adsorbed on Bronsted acid sites. These two bands disappear along with the appearance of a new band at 1429 cm-1, when deuterated alumina is pretreated at 400-degrees-C and subsequently subjected to ammonia. This new band at 1429 cm-1 is due to NH3D+ formed from ammonia adsorbed on acidic OD sites. Consequently, ammonia IR results demonstrate the existence of Bronsted acid sites on alumina pretreated at 400-degrees-C.