A computer program system has been developed for best estimate assessments of radiological consequences of accidental atmospheric releases of radionuclides. Computerized data bases as realistic as possible have been established and used describing weather sequences, land topography and usage, human population density, yield of agricultural products, etc. Input from the complex atmospheric transport program MUSEMET and from the food chain program ECOSYS is combined with the main program BAMBUS to calculate site specific probability distributions for individual and regional collective exposures as functions of the time of year of the release, the time after release, spatial location, exposure pathway, etc