AbstractChanges were studied in the bulk protein of tobacco leaves, lucerne shoots and sunflower‐seed kernels subjected to aerobic autolysis at room temperature. Bulk‐protein fractions from cigar and from commercial sunflower‐seed meal were also examined. Quinic acid, released by cold alkaline hydrolysis, was used as a measure of binding of chlorogenic acid residues to the proteins. On aerobic autolysis, the proteins of the leafy materials underwent some proteolysis; chlorogenic acid residues became bound to the protein, with concomitant diminution of free chlorogenic acid. The proteins showed browning, increased ultraviolet absorption and diminished content and “chemical availability” of lysine. However, during aerobic autolysis, the bulk protein of sunflower‐seed kernels did not couple appreciably with the chlorogenic acid congeners present; the above accompanying phenomena were also largely absent. It is concluded that, when protein‐rich plant materials are to be fed to monogastric animals, and particularly when their lysine content is critical, more attention should be paid to effects of the polyphenols and polyphenol oxidases present in the o