Abstract T lymphocytes bear insulin receptors only after activation and entry into the cell cycle. To determine whether cell motility is concomitant with growth factor action in T lymphocytes, we measured the chemotactic activity of porcine insulin (10(-11) to 10(-5) M) for T lymphocytes. We found that the chemotactic response of human T cells activated with phytohemagglutinin (PHA) to porcine insulin was increased over that of resting T cells, with a concomitant two log leftward shift in the dose response. CD4+ and CD8+ subsets responded identically. Checkerboard analysis showed insulin to be chemotactic, as well as chemokinetic. The nature and time course of acquisition of the dose-response shift suggest that chemotaxis may be signaled by insulin acting on high affinity insulin receptors. The chemotactic effect of insulin exemplifies the general chemotactic effect of growth factors for motile target cells, and may be a useful model for the study of chemotactic signaling in T lymphocytes.