Orange, lemon, grapefruit and tangerine juice con- centrates at 61 , 44.5 , 59 and 59.5 Bx, respectively, were obtained from one of fruit juice producers in Tur- key. All citrus juice concentrates in glass jars were stored in darkness at 28, 37 and 45 C for eight weeks. Ascorbic acid and HMF contents were determined every week and analyses were carried out on two replicates.