Intrinsically disordered proteins are very common in eukaryotes and thus understanding functional roles and factors which influence protein disorderness becomes very important. In this work, we ask whether global properties not directly related to the function of the proteins, like expression level and avoidance of aggregation, influence disorderness of proteins. We found that proteins expressed at higher levels tend to be less disordered, even within the same functional class. We also found that the correlation between expression level and evolutionary rate was significantly reduced for disordered proteins indicating the role of disorderness in preventing aggregation of highly expressed proteins, which are more susceptible to misfolding due to translational errors. We reconcile these seemingly opposing results based on the observation that the correlation between expression level and disorderness was significantly less for proteins involved in binding functions, suggesting that highly expressed proteins involved in binding functions utilize disordered regions to avoid aggregation. Our results show that disorderness is not just influenced by functional properties of proteins, but also by properties not directly related to their functions like expression level and avoidance of aggregation. (C) 2008 Published by Elsevier Inc.