A fraction of highly purified prolamellar bodies was isolated from etioplasts of wheat (Triticum aestivum L. cv. Starke II, Weibull), as previously described by Ryberg and Sundqvist (1982, Physiol. Plant., 56, 125-132). Studies on the protein composition revealed that only one major polypeptide of an apparent molecular weight of 36000 is present in the fraction of prolamellar bodies. This polypeptide was identified as the NADPH-protochlorophyllide oxidoreductase. The highest specific activity of the enzyme in etiolated leaf tissue was confirmed to be in the fraction of prolamellar bodies.