The present paper aims to search possible differences in effects due to low-level RF exposure to continuous wave in comparison to modulated RF field on the same carrier frequency, in vegetal tissues. This experimental study was focused on determination of some representative parameters for development of an agricultural plant species, Zea mays, whose seeds were previously exposed to non-thermal RF field in the 900 MHz band, in controlled conditions. Incident low-level continuous wave, amplitude modulated and frequency modulated signals were applied, while pigments concentration of chlorophyll a, chlorophyll b, carotenoids, nucleic acid concentration and average length of the plants in the 12^th day of development post-irradiation, were measured. A “thermal” reference constituted a very short duration exposure of one sample of seeds to 2.45 GHz high thermal field, while control unexposed sample was the absolute reference. The effects were different for continuous and modulated signals, but modulation has generally a lower impact in low-level exposures, and this was predictable