Veteran media watchdog Bagdikian has gone a long way--probably the farthest yet--toward pinning down the causes and consequences of media concentration. On some scores, he'll catch even the knowledgeable unawares. It doesn't come as a shock, though maybe it should, to read that 50 ""giant corporations"" control the majority of American media; it is discomfitting, however, to see the extent to which they ""exchange directors, and therefore have common policy views, with nonmedia corporations."" It's not startling, either, to be told that conglomerates resist anything that tarnishes their public image-until Bagdikian cites books canceled and reporters fired. The alarm bells go off and keep ringing, however, when he moves into his second major area of concern, the effect of mass advertising. From New Yorker editor William Shawn, Bagdikian learned that publication of Jonathan Schell's 1967 report on the village of Ben Suc (and subsequent, early anti-Vietnam War pieces) cost the magazine a 40 percent drop in advertising by 1970; as Bagdikian and Shawn observe, only a closely-held ""anomaly"" like The New Yorker could have held to its course under those conditions. (The advertising eventually came back.) Next, Bagdikian shows how mass advertising, concentrated in front-runner newspapers, creates one-newspaper cities--and then makes those very papers less responsive to a variegated public (and more attuned to high-income markets). Publishing for selected, affluent markets also results, on the political fronts, in ""a disparity between citizens' and merchandising needs""; the content becomes a vehicle for selling the goods. Looking around, Bagdikian foresees ""a collision between independent journalism and American corporate power."" Rousing, old-fashioned American reformism--on a topic that no one knows better than Bagdikian.