DNA from 6-day-old isolated pupal abdomens of silkworm, Bombyx mori, was clearly separated into three components designated as X 1, X 2 and normal DNA on MAK column chromatography. These DNA components were characterized by means of some biochemical techniques. All DNA components exhibited a hyperchromic effect when they were treated with either heat or alkali, whereas treatment with formaldehyde caused no increase in u.v. absorbance of those components. Thermal denaturation curves were also typical compared to those from double-stranded nucleic acids. Base compositions of the three different components were very similar to each other having G + C contents around 39 to 40%. The ratios of both A/T and G/C were nearly unity. Centrifugation in an ultracentrifuge showed that X 1, X 2, and normal DNA all migrated as a single peak with S 20,w of 4.6, 7.3, and 17.6, respectively. When mol. wt was estimated from the S 20,w, X 1, and X 2-DNA were found to decrease in size approximately to 1 60 and 1 15 respectively, of the normal DNA. In polyacrylamide gel electrophoresis, X 2-DNA showed a polydisperse migration pattern consisting of at least four broad bands, while X 1 and normal DNA were both detected as a single band, the former being a rather broad one. The mol. wt of four DNA components given from X 2-DNA on polyacrylamide gel were integral multiples of the mol. wt of the smallest DNA component, X 1-DNA. These facts strongly indicate that X 1 and X 2-DNA are degradation products of normal DNA, and suggest that subunit structure of chromatin may contribute to produce such DNA components.