Some biochemical characteristics of Israeli Jaffa Star Ruby ( red) and blond grapefruits were defined using atomic absorption spectrometry, antioxidant tests and the protein electrophoretic technique. It was found that the contents of dietary fibers, major and minor minerals, phenolic and ascorbic acids in both grapefruits were without significant differences. The contents of total polyphenols, anthocyanins and flavonoids were higher in red grapefruits, but also these differences were not significant. The antioxidant capacity was determined by two modified antioxidant methods, 2,2'-azinobis(3-ethylbenzothiazoline-6- sulfonate) radical cation (ABTS(+)) and scavenging activity against nitric oxide, and was compared with the Folin-Ciocalteu assay. The two antioxidant assays used have shown that the antioxidant potential of the Star Ruby ( red) grapefruit is higher than of the blond (P < 0.05) grapefruit. Proteins were extracted and separated. Some small differences were found in the sodium dodecyl sulfate-protein bands in the region of 36 kDa. Antioxidants and proteins can be used for characterization of the quality of grapefruits as a fruit diet