The cognitive abilities involved in the Connections (Salthouse, et al., 2000) version of the trail making test were investigated by administering the test, along with a battery of cognitive tests and tests of complex span and updating conceptualizations of working memory, to a sample of over 3600 adults. The results indicate that this variant of the trail making test largely reflects individual differences in speed and fluid cognitive abilities, with the relative contributions of the two abilities varying according to particular measure of performance considered (e.g., difference, ratio, or residual). Relations of age on trail making performance were also examined. Although strong age differences were evident in the Connections and working memory measures, with both sets of variables there was nearly complete overlap of the age differences with individual differences in speed and fluid cognitive abilities. (Contains 5 tables and 7 figures.)