I131 thyroid uptake after the Chernobyl's accident was sampled in a Val Pellice school. Children were grouped according to sex, age and area of residence. The procedure used in collecting data and calculating the transformation coefficients from activity counts by computer simulation is analysed, as are the errors and sensitivity of the method. The activities were then converted into doses using an intake model. The dose levels identified are lower than the estimates based on the measurement of environmental matrices. Statistical analysis revealed certain subgroups with significantly different levels of absorption: particularly groups accustomed to a different diet or living in particular areas.