A method is proposed for the estimation of longitudinal aerodynamic coefficients (parameters) of external stores through the technique of parameter estimation from flight test data. The release of stores acts as an input to generate flight test data which are analysed through an output error method, called the Gauss-Newton method, to estimate the store parameters. An example with simulated data has been used to show how the accuracy of estimation is affected by the varying noise level in the measured response, the initial values of parameters used, and the location of stores on the parent aeroplane, It is shown that for low noise levels, the so-called Method 1 can estimate aeroplane as well as store parameters in one single step. However, for high noise levels, the two step approach of Method 2 is recommended whereby the aeroplane parameters are first estimated separately and then the store parameters are obtained by analysing the aeroplane response to store dropping.