Object-Oriented design patterns are an emergent technology: they are reusable micro-architectures, high level building blocks.This paper presents a conservative approach, based on a multi-stage reduction strategy using OO software metrics and structural properties to extract structural design patterns from OO design or code. Code and design are mapped into an intermediate representation, called Abstract Object Language, to maintain independence from the programming language and the adopted CASE tools.To assess the effectiveness of the pattern recovery process a portable environment written in Java, remotely accessible by means of any WEB browser, has been developed. Based on this environment, experimental results obtained on public domain and industrial software are discussed in the paper.