After enzyme inhibition with methanol the original volatile compounds of the fruits were investigated in order to compare the quantitative composition of the aroma substances in orange fruits and juices. Aroma compounds of fresh, flash pasteurized and pasteurized juices were analysed. After aroma enrichment by liquid-liquid extraction, prefractionation of the flavor compounds by column chromatography on silicagel 56 flavor substances in the fruits and in the different juices were identified and determined by gas chromatography and mass spectrometry. In comparison to their content in the fruits only 10% of the terpenic hydrocarbons and about 30-66% of the esters were found on average in the fruits. Among the secondary flavor substances, which were not present or present only in traces in the fruits, but showed in juices concentrations up to 0,2 ppm, were 4-terpinenol, carveol and tr-2,8-menthadien-1-ol. After a thermic treatment also 3-hydroxy-2-butanone and 3-methyl-2-buten-1-ol were identified.