Three cDNA clones for acyl carrier protein (ACP) isolated from a λgt11 cDNA library prepared from greening barley seedling leaves using a 66'mer oligonucleotide probe have been sequenced. pACP 2 (371 bases) and pACP 11 (768 bases) code for the 90 amino acid chloroplast located ACP I. pACP 1 (520 bases) codes for a hitherto unknown protein with 83 amino acids that has been designated ACP III. The primary structure of its 27 amino acid partial transit peptide bears no obvious similarities to the transit peptide of ACP I. Northern analysis of immature caryopses' poly A⁺ RNA using the 66'mer probe reveals the presence of an ACP mRNA of significantly smaller size than the ACP mRNAs detectable in the leaf.