We have mapped the transcription start sites of three petunia rbcS genes and reassayed the relative expression levels of the petunia rbcS genes using the technique of primer extension. This analysis was performed specifically to address the confusion in the literature concerning the relative expression levels of the two petunia rbcS genes, SSU301 and SSU11A. The primer extension analysis reported here confirms our previous results, specifically that the rbcS gene, which we term SSU301, gives significantly higher levels of steady state RNA than any of the other rbcS genes in leaf tissue from 10 week old petunia plants.