The normal fog increase during storage of black-and-white silver halide materials is usually caused by exposure to background radiation from surrounding building materials. Cosmic radiation can normally be neglected. The fogging radiation is seldom homogeneous all over a room. Edge fogging and uneven distribution of fog arise inside the boxes from the absorption of radiation by the film sheets. Distribution and rate of increase of fog can be strongly influenced by the choice of building materials. It is recommended to keep the dose rate below 10 muR/hr in commerical stockrooms, below 3-4 muR/hr in rooms for sensitometric quality control. The importance of good ventilation for reduction of the radon gas content is emphasized. The influence of radiation fog on sensitometric data is discussed. A method for testing fogging sensitivity is outlined. Conditions during overseas transport, flights, and other transport are discussed. Temperatures up to 30°C have normally no significant influence on fogging of x-ray films. Complaints of fog usually arise from storage at higher background than 15 muR/hr. The guarantee clause on film boxes emphasizes cool and dry storage but does not define protection against gamma radiation. Natural background radiation can vary all over the world between 5 and 300 muR/hr. A dose rate of around 10 muR/hr should be prescribed as normal storage condition for the full validity of the expiration marking, as this is the most common background radiation level and is easily realized on most places.