Nuclear DNA content was determined in 17Rutaceaespecies. The results obtained suggest that both nuclear DNA content and mean chromosomal DNA content appear to be very sensitive indicators of the kin relationship between species or genera. The variation in nuclear DNA content amongRutaceaeis mainly determined by high ploidy levels. Diploid and tetraploid species generally have a 4C of less than 5.5 pg, whereas those with higher ploidy have a 4C of more than 12 pg. The few exceptions in this tendency are encountered in species from temperate regions where the evolutionary strategies at the chromosome level seem to diverge from those developed by tropical plants.