The juices of five grapevine cultivars cultivated in a typical Mediterranean climate were analyzed for sugars, organic acids, and phenols at four distinct stages of berry development. When the unripe berries were almost in full size, the glucose and fructose contents, based on HPLC detection, ranged from 13.3 to 30.7 g L-1 and from 8.3 to 23.7 g L-1 for 'Muscat of Alexandria' and 'Muscat of Hamburg', respectively. At this stage, tartaric acid concentration was between 10.3 ('Italia') and 12.3 g L-1 ('Muscat of Alexandria'), while the level of total phenols was low. Up to veraison, there were slight reductions in organic acids, while sugar content increased slightly. However, dramatic changes in all genotypes were apparent after veraison. Slight reductions were determined in the glucose and fructose levels of 'Italia' prior to final analysis, possibly indicating this cultivar's sensitivity to late harvest. In the final analysis, glucose and fructose content varied from 86.4 ('Italia') to 107.0 g L-1 ('Muscat of Hamburg'), and from 73.1 ('Italia') to 94.1 g L-1 ('Alphonse Lavallee'), respectively. Tartaric acid content of ripe berries was between 3.8 ('Alphonse Lavallee') and 5.2 g L-1 ('Isabella') with a mean value of 4.6 g L-1, and phenol content of mature berries ranged from 2,253 to 2,847 mg L-1. This study provides valuable information for further understanding the sugar, acid and total phenol changes that occur in some grape cultivars during berry maturation. Therefore, these results will be useful for future research on the biochemistry of the grape berry.