ment data during the 23-year residence interval. The results indicate that be- cause of urine activity concentration variability, there was a 60% probability that the male value for Re would be different from the female value by the factor observed. Thus differences in the derived activity ingestion rates and dose equivalents were not significant. Figure 14 shows a semi-log plot of the 6520 and 1376, activity ingestion rate histories for adults on Rongelap. A smooth curve was drawn between points, and the appearance of an increasing 1374, ingestion rate during the 1960's indicates the possibility of another contaminating event. The Hardtack Phase I se- ries was conducted just prior to the observed increase in the curve and fallout from the Cactus, Yellow Wood, and Hickory experiments detonated at Bikini and Enewetak would have reached Rongelap. However, several observations fail to sup- port the conclusion that recontamination was significant. These are as follows: 1) the increase in 1376, ingestion rate was not in conjunction with an increase of ar however, since O578 is an activation product it may have not been produced in the same proportions. 2) The peak 1376, body-burden at Utirik occurred nearly three years after the initiating event, Castle BRAVO, while the peak body-burden at Rongelap followed six years after the potentially contaminating experiments of the Hardtack series in 1958. 3) The activity inges- tion rate at Utirik demonstrated a continyously declining pattern versus the humped patternobserved at Ronge lap. This occurred even though there was an equal external exposure rate history following the Hardtack series as measured by the U.S. Public Health Service on both Rongelap and Utirik (Un59). 4) The peak exposure rate on Rongelap following the Hardtack series was 10,000 times less than the peak exposure rate following BRAVO. These facts suggest that the Hardtack series was not a major factor influencing the Rongelap body-burden 29