The oxidative stress theory of ageing predicts that animals living longer will have less cumulative oxidative damage together with structural characteristics that make them more resistant to oxidative damage itself. Although a general relationship between body size, metabolism and longevity does not exist in marine invertebrates, they are generally characterized by low rates of metabolism and reactive oxygen species (ROS) formation associated with lower antioxidant enzyme activities compared to vertebrates. Birds and mammals have very similar size-affected metabolic rates and their metabolic intensity explains only some of the variation in maximum lifespan potential (MLSP). Within each class, smaller animals have higher rates of metabolism and ROS production and membranes that are more susceptible to oxidative damage and autocatalytic propagation of free radicals than larger ones. Although the high variation in life-history strategies is accompanied by substantial variation in MLSP, there is a consistent positive correlation between rates of ROS formation and antioxidant levels among most animals examined so far for these traits. The consensus of these studies is that ROS and antioxidant levels are inversely related to MLSP. The lack of a clear stoichiometric relation between variables contributing to oxidative stress limits our capacity to infer longevity consequences from measures of pro-oxidant or antioxidant status among or within species. © 2010 The Authors. Journal compilation © 2010 British Ecological Society.