In literature quite a lot of data is available on uptake of radioactive caesium in mushrooms. There is less available on the evolution of concentration in fruitbodies after several years and on “outbound” transfer of radiocaesium from fruitbodies to their direct environment, i.e. dilution according to cooking techniques. The recent event at Fukushima has put the question of radionuclides in food, and the following exposure of consumers, high on the agenda. The purpose of this paper is twofold: (1) in order to investigate the variation in time of caesium uptake by fungi, analyses of the same species having grown on the same spot at different intervals during the last 25 years have been performed and (2) in terms of radiation protection the most important thing is the activity taken in by the consumer and not the contamination of raw products. Preparation can have a great impact on activity concentration. Various species of mushrooms frequently eaten have been sampled in Europe and contaminated areas in Japan. Different preparation techniques that can break the walls of the hyphae (drying, deepfreezing etc.) have been applied as well as different treatments: boiling or macerating in water with salt, in acid and basic media. The pH of different media was adjusted and measured. The samples and the medium were analysed separately in gamma spectrometry.