The compositions of commercially available fruit juices on the Slovenian and Cypriot markets have been compared and checked against the corresponding declarations on the packaging. Values of delta(13)C in the pulp, sugars, and ethanol (produced by fermentation and distillation) have been obtained by isotope ratio mass spectrometry and (D/H)(I) and (D/H)(II) ratios determined by Site-specific Natural Isotope Fractionation NMR and compared with literature data. These data show that some juices on the Slovenian and Cypriot markets were adulterated. Measurements of delta(18)O in the water and of (D/H)(II) in the ethanol indicated a significant difference in commercially available juices due to differences of the "tap" water in Slovenia and Cyprus, as most of the juices were diluted from concentrate. Using Principal Component Analysis, very clear differentiation can be made between juices from the two countries, arising from their distinct aquatic environments and climates. The identification of botanical origin of fruit juices was possible only in the case of Slovenian orange and apple fruit juices.