[en] The influence of different sea water treatments on radio-isotope flux rates was tested in three species. For any one species no significant differences in "6"5Zn loss rate were noted between organisms held in sea water collected in situ and in those maintained in sea water from the laboratory system. Increased sea water zinc concentration accelerated "6"5Zn flux rates; however, the more rapid "6"5Zn loss compared to that measured in control sea water was only significant when the concentration was increased by 100μg zinc/liter. Simultaneous laboratory and field experiments indicated that loss rates in clams and mussels were similar whether animals were held in the field or in the laboratory. Experiments in which crabs were monitored for "6"5Zn loss gave conflicting results. One experiment performed during the summer indicated that crabs lost "6"5Zn significantly faster in the laboratory than in the field. Another experiment performed during the winter when water temperatures were lower indicated no differences in loss rates between the two systems. Differences in radioisotope flux rate may have been related to the intermolt cycle; nevertheless, it was concluded that for certain organisms care should be exercised when applying results of laboratory experiments to the field situation. (author)