A seedling, designated M.A.701, remarkable for its vigor and resistance to rust, was discovered during the fourth year of selection of Japanese mint (Mentha arvensis L. subsp. haplocalix Briquet var. piperascens Holmes or forma piperascens Malinvaud). The botanical characters of the variety derived from this seedling, especially the vegetative habit and colouring of leaves and stems, make it quite different from the original variety. This difference is enhanced, when we compare the nature of the essential oil components of "Campinas" M.A.701, as described in the present paper, with that of the common Japanese mint. The higher yield of the new variety, compared with that of the common Japanese mint, was soon confirmed by the first cultivators, to whom small quantities of rhizomes were sent for experimental planting. About 12 hectars were cultivated em 1949/50 and about 900 hectars in 1950/51. It is expected that the new variety will, on account of its greater economic value, tend to replace entirely the Japanese mint generally grown in the State of São Paulo.