A precise technique to measure DNA content in M. douglasii (D.C.) Sch.-Bip., Price and Bachmann (PB) strain A26 was reported. Relative absorbancy (560 nm) of Feulgen-stained spherical nuclei, arrested at the 2C DNA level, was measured microspectrophotometrically. Relative DNA contents were determined by placing epidermis of an inbred line on the same slide with epidermis from the unknown sample prior to hydrolysis and staining. The DNA values were adjusted to the internal standard; direct comparisons were made of values collected from different slides and staining batches. Differences among individual plant specimens in the 2.5%-5% range are detectable with this procedure. Intraspecific variation up to 20% in DNA content was apparent.