Аннотация:A search for long-term trends in the F2 layer critical frequency foF2 is performed based on verticalsounding observations at three stations of the Northern Hemisphere (Juliusruh, Boulder, and Moscow) andthree stations of the Southern Hemisphere (Townsville, Hobart, and Canberra). A method developed andextensively described by the authors is used. The data for two winter months in each hemisphere for five nearnoon LT moments were analyzed. Three solar activity (SA) proxies (F30, Ly-α, and MgII) were used to eliminate SA effects. Negative trends are obtained for all considered situations (station, month, LT moment, SAproxy). The trends agree well with each other both if stations of the Northern and Southern hemispheres arecompared individually or in aggregate.