Human tissues, obtained at autopsy in several geographical locations in the United States exposed primarily to atmospheric fallout from weapons testing and those from individuals who formerly worked with plutonium, have been analyzed quantitatively for plutonium in a continuing study at the Los Alamos Scientific Laboratory. This article contains additional data accumulated since publication of LASL report LA-4875, “Plutonium in Autopsy Tissue”, in 1973 and includes some reanalyses of questionable results included in that report. The primary objectives of the present study are to determine the baseline concentrations of plutonium in the general population and to monitor for changes that may be related to growth of the nuclear industry; obtain data on the long-range time dependence of fallout plutonium incorporation into the body; determine plutonium distribution in the body from various routes of intake; and provide a means for evaluating the validity of in vivo estimates of plutonium body burdens in occupationally exposed workers. The tissues analyzed include lung, tracheobronchial lymph nodes, liver, bone, kidney, and recently, gonads, thyroid, and spleen. The median concentrations observed in the general population (dis/min per kg of tissue wet weight) are: tracheobronchial lymph node (360), 5.8; liver (701), 1.6; vertebrae (325), 0.6; rib (95); thyroid (184), 0.6; lung (705), 0.4; gonad (264), 0.3; spleen (325), 0.2; and kidney (631), 0.1. The parenthetical numbers indicate the number of samples analyzed. The results of the analyses of tissues from occupationally exposed workers are reported in a subsequent article.