Chlorophyll a is a key-compound in the process of light absorption in the photosynthesis. Monitor the chlorophyll a fluorescence to obtain information about the photosynthetic apparatus of energy production is attractive because the chlorophyll a fluorescence could be detected without destruction of the source. Studies performed by the Laboratório de Hidrobiologia (UFRJ) and by the Laboratório de Monitoramento Ambiental Remoto (LabMAR) (PUC-Rio) in marine water samples indicated a linear relation between the absolute values obtained by the former for the chlorophyll a concentration and the relative values obtained by the latter for the chlorophyll a fluorescence. This result motivated both laboratories to obtain absolute values for the chlorophyll a concentration, in marine water samples, as confident as possible and, then, relate these values to the relative values generated by the LIDAR-PUC. In this way, the introduction of a quality control program in the Laboratório de Hidrobiologia indicated that this laboratory is able to analyse marine water samples and to obtain confident values for the chlorophyll a concentration by fluorimetry. However, a more rigorous evaluation of the relation between the chlorophyll a fluorescence and the respective confident value for the chlorophyll a concentration is still necessary.