Abstract. Software performance engineering deals with the consideration of quantitative analysis of the behaviour of software systems from the early development phases in the life cycle. This paper summarizes in a semiformal and illustrative way our proposal for a suitable software performance engineering process. We try to integrate in a very pragmatic approach the usual object oriented methodology --supported with UML language and widespread CASE tools-- with a performance modelling formalism, namely stochastic Petri nets. A simple case study is used to describe the whole process. More technical details should be looked up in the cited bibliography.