Stimulation of T cells through the T-cell receptor results in the activation of a series of signaling pathways that leads to the secretion of interleukin (IL)-2 and cell proliferation. Influx of calcium (Ca(2+)) from the extracellular environment, following internal Ca(2+) store depletion, provides the elevated and sustained intracellular calcium concentration ([Ca(2+)](i)) critical for optimal T-cell activation. Our laboratory has documented that exposure to the herbicide 3,4-dichloropropionanilide (DCPA) inhibits intracellular signaling events that have one or more Ca(2+) dependent steps. Herein we report that DCPA attenuates the normal elevated and sustained [Ca(2+)](i) that follows internal store depletion in the human leukemic Jurkat T cell line and primary mouse T cells. DCPA did not alter the depletion of internal Ca(2+) stores when stimulated by anti-CD3 or thapsigargin demonstrating that early inositol 1,4,5-triphosphate-mediated signaling and depletion of Ca(2+) stores were unaffected. 2-Aminoethyldiphenol borate (2-APB) is known to alter the store-operated Ca(2+) (SOC) influx that follows Ca(2+) store depletion. Exposure of Jurkat cells to either DCPA or 50 microM 2-APB attenuated the increase in [Ca(2+)](i) following thapsigargin or anti-CD3 induced store depletion in a similar manner. At low concentrations, 2-APB enhances SOC influx but this enhancement is abrogated in the presence of DCPA. This alteration in [Ca(2+)](i), when exposed to DCPA, significantly reduces nuclear levels of nuclear factor of activated T cells (NFAT) and IL-2 secretion. The plasma membrane polarization profile is not altered by DCPA exposure. Taken together, these data indicate that DCPA inhibits T-cell activation by altering Ca(2+) homeostasis following store depletion.