A chlorophyll fluorescence analysis has been performed in Euglena gracilis using a portable PAM fluorometer. For analyses, the cells were collected on glass-fiber filters. The method employed allowed confirmation of the special properties characterizing the chlorophyll fluorescence emission in the organism. Most interesting aspects were the induction of non-photochemical quenching in darkness, the good ability to maintain PSII open over a wide range of irradiances and the dissection of three components originating in the non-photochemical quenching (energy, state transition and photoinhibitory quenching). Under high irradiances, photoinhibition of PSII units played a key role in determining non-photochemical quenching. For this reason, during relaxation only a partial recovery of PSII quantum yield was observed. Since the results were consistent with the data available in literature, with only some discrepancies due to different experimental procedures, the use of the portable PAM fluoro-meter can be proposed as a valid alternative to conventional PAM fluorometers for the study of fluorescence properties in flagellate algae.