We examined cytotoxicity of replication-competent type 5 adenoviruses (Ad5) in human pancreatic carcinoma cells with a p53-defective genotype. The replication-competent Ad5 of which E1A gene was activated by exogenous transcriptional regulatory sequences, derived from the midkine and survivin genes, achieved cytotoxicity to the pancreatic carcinoma. These cells were susceptible to replication-incompetent Ad5 expressing the wild-type p53 gene. We also produced the replication-competent Ad5 bearing the same exogenous regulatory sequences and the type 35 Ad-derived fiber-knob region, and showed that the cytotoxicity was comparable to that of the replication-competent Ad5 prototype. We then investigated possible combinatory effects of the fiber-modified replication-competent Ad and Ad5 expressing the wild-type p53 gene, both of which did not interfere respective infections. The combination produced synergistic cytotoxic effects with enhanced cleavages of caspase-3 and PARP molecules, and with increased sub-G1 fractions and annexin V-positive populations although the viral production of the replication-competent Ad was rather suppressed by expressed p53. Pancreatic cells infected with both Ad showed increase of p53 and decrease of MDM2 and p21 levels, compared with those infected with Ad expressing the p53 gene. These data collectively indicated that replication-competent Ad augmented susceptibility of pancreatic cells to apoptosis through upregulated p53 expression.