The specific activity of ⁶⁵Zn (nanocuries ⁶⁵Zn/g total Zn) was determined in various organs of the common coastal mussel, Mytilus californianus Conrad, collected from six locations along the Pacific Coast. These organs included the gills, mantle, foot, reproductive organs, adductor muscle, and viscera. After ashing and dissolving with nitric acid (8 M), each tissue was analyzed for ⁶⁵Zn by gamma-ray spectrometry. The determination of total zinc concentrations of the various organs was accomplished by atomic absorption spectrophotometry as well as by neutron activation analysis. Variable amounts of both stable zinc and radioactive ⁶⁵Zn were observed within the specific tissues from a given location. The ⁶⁵Zn specific activities of the tissues of organisms from a particular station however, tended to be uniform, at least within the uncertainty of the measurements. Both radiozinc and ⁶⁵Zn specific activity decreased with distance from the Columbia River mouth, whereas the stable zinc tended to remain uniform for a specific tissue. Tissues high in radiozinc were also high in stable zinc and conversely. An estimate of the input specific activity from the mussel' environment (food and/or water) was calculated from a simple model resulting in a value similar to zooplankton values sampled from within the Columbia River plume. Comparison of the concentrations of zinc determined by neutron activation with those determined by atomic absorption spectrophotometry indicated a linear relationship between the two methods. Results of atomic absorption measurements were approximately 27% larger than the results of neutron activation analysis, indicating the presence of a systematic error. The higher values attained by atomic absorption are attributed to evaporation during storage of the ash solution which would lead to an increase in zinc concentration. In considering the two methods of analysis, economy of both time and expenses favors the atomic absorption method over that of neutron activation. / Graduation date: 1971