We have established three clonal lines of oregano (Origanum vulgare) for the purpose of investigating the possible link betweende novosynthesis of proline and the phenylpropanoid pathway. We usedPseudomonasas inoculation in the otherwise sterile micropropagated oregano shoots to stimulate a defense response. Oregano clones, like other plants, carry out an elicitor‐mediated defense response by inducing the phenylpropanoid pathway. Free phenolics and rosmarinic acid are produced via this pathway. We measured free proline, rosmarinic acid, and free phenolics in oregano shoots. We found that the induced higher levels of rosmarinic acid in somePseudomonasinoculated clones and at several stages is often correlated to higher levels of proline in those same clones. We found no conclusive link between free phenolics and free proline levels. From this study clonal line 0–4 appeared to be the best line to investigate the role of proline‐linked pentose phospahte pathway in regulating rosmarinic acid synthesis.