Highly specific neutron activation analysis procedures involving post irradiation chemical separations were developed for the determination of Cu, Hg, Zn, Cd, As, Se and Cr in fish tissues. The procedures developed were used to determine the levels of these biologically active elements in some of the commercially important fish species of Lake Erie. The nuclear analytical procedures developed generally involved the irradiation of fish tissues followed by wet-ashing in the presence of nonradioactive carriers From the homogeneous solution of the tissue digest, the elements of interest were chemically isolated and the radio-activities were measured by scintillation gamma ray spectrometry. The results reported include both the determination of the precision and accuracies of each of these elemental analyses and a survey of these seven elements in nine major fish species of Lake Erie.