AbstractT lymphocytes are activated by a complex series of events, but the mechanisms remain unclear. One uncertainty is the time of receptor‐ligand interaction necessary for commitment to DNA synthesis and proliferation. Although this issue has broad implications for the interpretation of T cell activation data, it remains unresolved. Therefore, we examined the temporal activation requirements of rat splenocytes stimulated with con‐ canavalin A (Con A) by measuring proliferation, as well as interleukin‐2 (IL‐2) production and IL‐2 receptor (IL‐2R) expression. Splenocytes stimulated with various Con A concentrations for 3 h did not incorporate significantly more [3H] thymidine than unstimulated splenocytes. Some increase occurred after 6 h of lectin exposure but maximum proliferation occurred only after the 52‐h stimulation. Furthermore, Con A incubations of 6 h or more were required for significant increases in IL‐2 or IL‐2R. Maximum lymphokine production and receptor expression were observed after the 52‐h stimulation. Thus, activation of some primary lymphocytes required only 6 h of stimulation, but much longer mitogen contact was necessary for maximum recruitment.