In order to determine the exact age by radiocarbon methods, it is necessary to know the cosmic ray intensity at the sample location, the temperature of the sample when it was col-lected and the depth at which the sample occurred, the C isotope composition at the surface of the material enclosing the sample, the age determined by a nonradioactive method, and the present activity of ₁₄C in the atmosphere. Soils, rocks, wood, marine sediments, and archaeo-logical samples were studied. -- AATA