Immediately after pollination female flowers of asparagus plants were treated with ethyl methanesulfonate for selection of mutants resistant to 5-methyltryptophan (5MT), and seeds (M1) were obtained after 3 months. The M1 seeds were lighter and snowed a lower germination rate respect to control seeds. Various morphological mutations were observed in the Ml seedlings and many of them had longer cladophylls and shorter internodes than control plants. Meristems originating from the Ml plants were cultured on medium containing 5MT. Selection based on the shoot growth index was carried out after 3 weeks, and a few 5MT-resistant lines were selected among culture lines.