Bradykinin gave a biphasic increase in intracellular free Ca2+ concentration ([Ca2+]i) in serum-deprived Swiss 3T3 fibroblasts loaded with the photoprotein aequorin. Epidermal growth factor (EGF) alone did not increase [Ca2+]i, but when added after bradykinin there was an increase in [Ca2+]i. The EGF-dependent increase in [Ca2+]i was maximal at 3 min and disappeared with a half-life of 6 min after bradykinin. Removing Ca2+ from the external medium did not abolish either the bradykinin or the EGF-induced [Ca2+]i responses. Although prostaglandins E2 and F2 alpha also gave [Ca2+]i responses and permitted an EGF-dependent [Ca2+]i response, the effect of bradykinin did not appear to be mediated by prostaglandins since it was not blocked by indomethacin. Vasopressin and phorbol 12-myristate 13-acetate both gave a [Ca2+]i response but did not facilitate a [Ca2+]i response by EGF. Bradykinin or EGF alone did not increase DNA synthesis in growth-arrested Swiss 3T3 fibroblasts, but EGF added together with, or after, bradykinin increased DNA synthesis. The effect disappeared with a half-life of 180 min after the addition of bradykinin. It is concluded that stimulation of receptor protein tyrosine kinase is unlikely, by itself, to explain the increase in DNA synthesis produced by EGF. The observed increase in [Ca2+]i caused by EGF after bradykinin probably reflects the interaction of intracellular second messenger pathways leading to facilitation of DNA synthesis.