Chlorella ellipsoidea was incubated in nitrogendeficient medium to examine the changes in the relative DNA content per nucleus, which were measured by epifluorescent microspectrophotometry combined with Feulgen-pararosaniline staining. The results were compared with synchronous multiplication in the basal medium. The minimum and maximum measured DNA values per nucleus were 2.5 and 280, which were related to 1 C and 112 C respectively. The mode of the DNA value moved reciprocally between 8 C and 4 C levels under multiplication in basal medium, which one mother cell producing four autospores in each synchronous division. The average value of the modes over 5 days of nitrogen starvation was 8 C. The frequency distribution of the relative DNA value consisted of at most five levels, 1–3.2 C, 4–12 C, 28 C, 32 C, and 40–112 C. The modal changes suggested the occurrence of DNA synthesis caused by some intracellular nitrogen pools. During the nitrogen starvation, 10-fold cell multiplication and a small amount of cell growth occurred.