Posttranslational lysine acetylation is believed to occur in all taxa and to affect thousands of proteins. In contrast to the hundreds of mitochondrial proteins reported to be lysine-acetylated in non-plant species, only a handful have been reported from the plant taxa previously examined. To investigate whether this reflects a biologically significant difference or merely a peculiarity of the samples thus far examined, we immunoenriched and analyzed acetylated peptides from highly purified pea seedling mitochondria using mass spectrometry. Our results indicate that a multitude of mitochondrial proteins, involved in a variety of processes, are acetylated in pea seedlings.