This is a report on an inquiry into some of the social/political/ecological problems of the national parks of the United States. The authors examined the impact of man on the national parks and concluded that the parks now face dangers from within, in addition to the older and more generally recognized external pressures for economic exploitation of the parks' timber and mineral resources. These new dangers come from an increasing number and density of people, who spend more of their increasing leisure time in the parks and bring more of their automobiles and other equipment into the parks. This report is divided into five main sections: (1) the nature of a national park, (2) the national park resource, (3) development, (4) management of plants and animals, and (5) the concept of wilderness in national parks. This report is illustrated by 15 black and white photographs of various national parks in the country. (LC)