We examined the effect of pyrrolidine dithiocarbamate (PDTC), which potently blocks the activation of nuclear factor κB (NF-κB), on the induction of apoptosis by a variety of agents. Treatment of a human promyelocytic leukemia cell line, HL-60, with 10 μg/mL etoposide or 2 μM 1-β-d-arabinofuranosylcytosine induced NF-κB activation within 1 hr and subsequently caused apoptosis within 3–4 hr. The simultaneous addition of 50–500 μM PDTC with these agents blocked NF-κB activation and completely abrogated both morphologically apoptotic changes and internucleosomal DNA fragmentation for up to 6 hr. However, PDTC failed to inhibit the endonuclease activity contained in the whole cell lysates. The inhibitory effect of PDTC was also observed in etoposide-and dexamethasone-induced apoptosis in human thymocytes at a concentration of 1–10 μM. Since PDTC has both antioxidant and metal-ion chelating activities, we tested the effects of N-acetyl-l-cysteine (NAC)(antioxidant) or o-phenanthroline (OP)(metal-ion chelator) on the induction of apoptosis. Pretreatment of HL-60 cells or thymocytes with 100–500 μM OP for 2 hr, but not 10–60 mM NAC, suppressed subsequent occurrence of apoptosis induced by etoposide. These results suggest that the activation of NF-κB plays an important role in the apoptotic process of human hematopoietic cells.