The low-fluence-rate response of light-oriented chloroplast movement in Dryopteris sparse protonemata was induced by continuous irradiation with either red (R) or blue light (B). Effects of concomitant irradiation with far-red light (FR) indicated that the photoreceptor of R was phytochrome and that of B, a specific B photoreceptor. Action dichroism of light suggested that the absorption axes of the R-absorbing form of phytochrome and the B photoreceptor were parallel to the cell surface, and that of the FR-absorbing form of phytochrome (P fr), perpendicular. When irradiation was terminated, the B-induced chloroplast arrangement began to decay immediately. In contrast, the R-induced arrangement survived for approximately 3 h, but when R irradiation was terminated with an FR pulse, the decay began after 1 h. When R irradiation was terminated before the response reached the maximum, it stayed at the attained level for 3 h, but did not increase further. These results suggest that the R induction of chloroplast movement required not only the presence of a P fr gradient, but also the continued asorption of R, the former is only effective in determining the direction of the movement and in holding the chloroplasts at the area of higher P fr concentration.