DA/DAPI and C chromosomal heteromorphic sites (1q, 9q, 15p, 16q, Yq) in a sample of 136 unrelated individuals from the Garfagnana valley (Tuscany, Italy) have been analyzed quantitatively and qualitatively. The variations in length, between-homolog heteromorphisms, and intensity of fluorescence of the heterochromatic bands have been compared in two subsamples of the population (upper and middle valley) individualized according to geodemographic criteria. DA/DAPI heterochromatin differed significantly from C heterochromatin, showing a lower average amount and a higher variability at each site. This suggests a differential staining of DNA of the two banding systems. Furthermore, DA/DAPI heterochromatin was less uniformly distributed in the population than C heterochromatin and the regions 16q and Yq discriminated better between subsamples. The variations of DA/DAPI fluorescence at the 15p site demonstrated an excess of homomorphic individuals in the upper valley, which could be related to the mating structure of the population living in this area.