Greek yogurt has become much more popular within the last 15 to 20 years. The by-product of Greek yogurt manufacture is acid whey. Although acid whey has been considered a waste product, researchers are exploring various uses of this whey. Since the health benefits of consuming probiotics are widely known, one may propose adding probiotics to acid whey to form a probiotic beverage. Typically, probiotic bacteria do not thrive in acidic conditions.It would be beneficial to determine if the probiotic Lactobacillus acidophilus can survive in these acidic conditions. The objectives were to determine the growth of L. acidophilus in acid whey resulting from manufacturing Greek yogurt and to study any changes in apparent viscosity, pH, and titratable acidity over 4 weeks of refrigerated storage. Plain yogurt was manufactured, and whey was separated from plain yogurt to yield Greek yogurt and acid whey. Acid whey was batch pasteurized, cooled, sweetened, flavored with pineapple flavoring, inoculated with L. acidophilus, and stored at 4˚C for 4 weeks. The log L. acidophilus counts progressively decreased from 7.84 immediately after manufacture to 2.06 at week 4. There were no significant changes in pH and titratable acidity of the pineapple-flavored probiotic acid whey over 4 weeks of storage, indicating product stability over shelf life. Viscosity changed over the storage time with minimum values at week 2 and maximum values at week 4. Although the counts declined over 4 weeks of storage, some L. acidophilus survived in the pineapple-flavored acid whey.