An application of the two-paramenter logistic (Rasch) model to tailored testing is presented. The model is discussed along with the maximum likelihood estimation of the ability parameters given the response pattern and easiness parameter estimates for the items. The technique has been programmed for use with an interactive computer terminal. Use of the procedure is described in a flexible achievement testing setting. Results are presented showing the number of items needed for good estimation. The independence of items used and ability estimation is shown. Applications of the system to intelligence testing are discussed. (Author)