The mechanism of photosynthesis, environmental conditions, and the chemical and biological significance of photosynthetic bacteria are discussed. Photosynthetic bacteria, which are extremely useful and important in the ecological system, can become a cause of pollution when excessively proliferated. The idea that pollution could be solved by planting vegetation is also a misconcept. Carbon dioxide is not the major source of pollution, and local increases of CO/sub 2/ partial pressure do not affect the environment in general. More important, green plants are sensitive to air pollutants and react faster than any other living things to pollutants such as fluorides, nitrate, ozone, peroxyacetyl nitrate, and sulfur dioxide. Only 1-3% of solar energy is used for photosynthesis. The use must be increased to maximum by effective planning of plant formation, density, and arrangements. Through genetic studies, production and proliferation of useful plants should be planned and developed. Pollution control must be programmed ecologically, suitable ecological systems must be developed in various geographical areas, in addition to the effort to eliminate pollution sources.