Recombinant interleukin (IL)-15, derived from a simian kidney epithelial cell line, is a chemoattractant for human blood T lymphocytes judged by its ability to increase the proportion of cells in polarized morphology, to stimulate invasion of collagen gels containing IL-15, and to increase the proportion of locomotor cells observed by time-lapse videorecording. The ability of lymphocytes to respond was partly, but not completely, inhibited by pretreatment with anti-IL-2 receptor beta-chain. The activity of IL-15 was completely abolished by preincubation with aIL-15 but unaffected by preincubation with aIL-2. No response of monocytes, neutrophils, or B lymphocytes to IL-15 was observed.