The in vitro chemotactic activity of chemokines have been well documented. However, study of their in vivo effects where components of rolling, adherence and diapedesis are pre-requisites to leukocyte infiltration have not been examined in higher species. In this study, we examined the biological activity of the CC chemokine, MIP-1alpha, in rhesus monkeys. Following an intradermal injection, a significant cellular infiltrate and an increase in the number of inflamed vessels were observed. This response peaked at 24 h and was sustained for up to 48 hours after injection. Phenotypically, the specific infiltrate consisted exclusively of CD68+ monocytes with no increase in other cell types over the saline injected controls. These studies represent the first examination of the in vivo effects of MIP-1alpha in higher species and indicate that MIP-1alpha is a selective monocyte recruiting agent in vivo.