Photobleaching and dark-bleaching of Euglena gracilis chloroplast fragments were studied at different pH. Moreover, the effect of these processes on low-temperature fluorescence was investigated. The photobleaching of the long-wave chlorophyll a forms C„704 and Cn692 proceeded at a higher rate than that of the C„681. C«672, and C„664 forms. Chlorophyll b is considerably more stable towards this process than the C„ components. At pH 7.10 the absorption around 649 nm even increased. The percentual quenching of fluorescence was much higher than the absorbance decreases. The dark-bleaching patterns of the C„704 and C„692 forms showed mutual differences. Moreover, they differed from those of the remaining C„ forms. Dark-bleaching of chlorophyll h did not notably diverge from that of the latter C„ forms. The percentual fluorescence decline was much higher than the decreases of absorbance also here. The results are discussed