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An extensive data base of vascular plant records (917 species, 71,062 records) was analyzed with the aid of a geographical information system (CIS) in an attempt to quantitatively characterize regional patterns of variation in the Israeli flora. The records were summarized in the form of a grid based site x species matrix, where each site represents a grid cell of 10 x 10 km. A total of 231 grid cells representing the entire area of Israel was included in the analysis. The 231 x 917 matrix was subjected to PCA ordination, and the loadings of the grid cells on the first principal component were used to construct a contour map of floristic variation. The patterns obtained indicate that the flora of Israel consists of two major territories : a mesic one (mean annual rainfall greater than 400 mm), and an arid one (mean annual rainfall lower than 200 mm). These territories are separated by a narrow transition zone characterized by steep floristic gradients. These results are consistent with the hypothesis that regional variation in rainfall is important in structuring the flora of Israel. The clear patterns obtained and their consistency with previous studies on the distribution of plants in Israel suggest that the analytical approach employed in this study may serve as a powerful tool for the identification of large-scale patterns of floristic variation.