Sixteen segments of Arabidopsis thaliana DNA that function as enhancers in transgenic tobacco plants were isolated using the pROA97 enhancer cloning vehicle and library transformation of Nicotiana tabacum. The sequences were compared for AT content, homology, repeated motifs, and expression pattern in transgenic N. tabacum. The sequences were average with respect to the AT content of A. thaliana DNA. They could be placed into seven homology groups. Five of the sequences are single-copy sequences. The remaining eleven sequences represent two homology groups. Homology Group I contains seven sequences with minor differences. Homology Group II contains four sequences with minor differences. Two repeated motifs were identified (5'-CCTCT-3' and 5'-AAGGAT-3'). Both repeated motifs are found in other plant enhancers, and in the promoter region of the cauliflower mosaic virus 35S gene. In the 35S gene TATA region, the motifs can form two alternative stem-loop structures. The TATATAA sequence is located in the loop region of both stem-loop structures.