Mathematical models are useful tools for studying many problems in the environmental and public health area. For a reliable development and application of these models modelanalysis has to be an indispensable part of the total modelling process. This modelanalysis usually consists of performing sensitivity- and uncertainty analyses to the model. In this report a methodology is presented for these analyses and a survey is given of available techniques. Moreover some currently used measures for quantifying the uncertainty contribution of the various sources of uncertainty are critically evaluated and improved.<br>