Quantitative determinations of the four black currant anthocyanins, cyanidin 3-O-β-glucoside, cyanidin 3-O-β-rutinoside, delphinidin 3-O-β-glucoside, and delphinidin 3-O-β-rutinoside, were achieved in black currant juices by a rapid and sensitive high-performance liquid chromatographic (HPLC) method. The method was validated, and quantification of anthocyanins in 13 commercially available black currant beverages was demonstrated. To optimize the handling of anthocyanin-containing samples, the pH-dependent stability of the anthocyanins was investigated. Four anthocyanins were incubated for 24 h in aqueous solutions at 13 different pH levels between 0.6 and 5.2, after which the samples were analyzed by HPLC. More than 90% of each anthocyanin remained intact up to pH 3.3. At pH 3.8 a local minimum in stability was detected, and at pH >4.5 the stability rapidly decreased. The antioxidant capacity of all 13 black currant juices was investigated by TEAC and FRAP, and the antioxidant potential of both the anthocyanin and the vitamin C contents in the juices was evaluated. This indicated that <70% of the antioxidant capacity of the juices could be attributed to the anthocyanin content or to vitamin C, signifying that other very potent antioxidants are present in commercial black currant juices.