Measurements of the chlorofluorocarbons CCl3F (F-11) and CCl2F2 (F-12) made in the subsurface anoxic zones of the Black Sea and Saanich Inlet, B.C., Canada show a pronounced depletion of dissolved F-11. These zones are strongly reducing and are characterized by the absence of dissolved nitrate (NO-3) and the presence of hydrogen sulfide (H2S). Models incorporating the atmospheric input histories of these CFCs and the observed distributions are used to estimate residence times for water in these zones and first order in situ removal rates for F-11. In contrast, measurements in the mid-depth low-oxygen zone of the eastern Pacific (where NO-3 is present and H2S is below detection limits) do not show evidence of similar rapid F-11 removal. ¿ American Geophysical Union 1995