pn Abstract Data on worldwide fallout of radioactive debris from the Castle series of weapons tests conducted in the Spring of 195k are summarized. Total world fallout of Beta activity to August 31, excluding the vicinity of the test site, is estimated at 7.1 megacuries, extrapolated to 1/1/38. During March, April and May the average monthly fallout was 1.5 mazacure les. During June and July it was at about half this level but in assist it increased to 1.2 megacuries.