This paper describes the MetaBuilder system: a means of constructing CASE tools by graphically assembling OO components. MetaBuilder belongs to a class of software systems known as metaCASE systems. Certain problems which can occur when attempting to build metaCASE tools are discussed and a solution based upon the use of an OO approach to designing such systems and of persistent object techniques for their implementation is proposed Details are given of the implementation of the proposed solution as well as examples of its use.