The report outlines the technical issues related to the estimation of measurement uncertainty (MU) involved in the GMO sector. In particular it gives guidance to GMO testing laboratories how to estimate the analytical variability of quantitative analytical results obtained by real-time PCR. Two selected approaches for the estimation of MU are presented in detail; references to alterntative approaches are given. The first approach presented in detail is using data from collaborative trial in combination with in-house quality control data for the estimation of MU. An alternative approach using data from within-laboratory samples for the estimation of MU is presented.