Two samples of ocean water from the Pacific, one collected at the surface near the coast outside San Diego Bay in the summer of 1956 and the other taken at a depth of 3500 m from longitude 124 d 41.0' W, latitude 33 d 54.5' N on March 25, 1957, were analyzed for total thorium alpha activity. The method of analysis is described, and the results are tabulated. Some information concerning the approximate isotopic composition of the thorium which was isolated from the surface water sample was obtained by observing the change in its alpha activity with time. The observed activities and the calculated values are given and are in good agreement. (J.S.R.)