The relationships among stability, maturity and complexity of ecosystems have been studied for many years. These ecosystem attributes are important in ecological theory and also for the appropriate management of resources. In a previous work, we proposed the U index, which accounts for complexity and recycling of detritus, and measures maturity in ecosystems according to attributes of E. P. Odum's theory of ecosystem development. Here we compare the behaviour of the U index and its ability to measure stability. Using models of ecosystems, we simulated disturbances and measured stability through resistance, persistence, resilience and recovery time, We found that the index is correlated with these attributes, but in an inverse way to that expected; that is, immature ecosystems were more stable and stability decreased when the systems matured. (C) 2001 Elsevier Science B.V. All rights reserved.