A case-representation paradigm developed in studies of medical expertise (Patel & groen, 1986; Boshuizen & Schmidt, 1992) is used to examine 5 engineers' initial representation of problems in a mineral wool production plant. Propositional analysis shows expertise effects in recall of case material and use of basic process control knowledge. A second experiment with identical methodology and 13 engineers at three levels of industrial experience reveals the expert engineers' infrequent but coherent use of central basic concepts. Basic knowledge seems to be consistently applied, also when they are asked to propose solutions to the problems. In contrast, Ph.D. -students and advanced students initially represent problems solely by using basic process control knowledge, but then propose unrelated and industry oriented solutions, based on information on the plant and process as presented to them in the case material.