We investigated the effect of 5-aza-2'-deoxycytidine (ADC) (a specific inhibitor of DNA methylation) on differentiation, Lewisy (Ley) antigen expression, and DNA fragmentation (a biochemical marker of apoptosis) in human pancreatic cancer MIA PaCa-2 cells. ADC markedly inhibited the growth of MIA PaCa-2 cells. Flow cytometric analysis showed that ADC suppressed the cell population in the G1 phase, but enhanced it in the G2/M phase. On the other hand, several markers of cell differentiation including morphological and biochemical alterations were distinctly induced in cells treated with ADC. Morphologically, the cells were enlarged and thinner than the untreated control cells, and intracellular alkaline phosphatase (ALP) activity was markedly increased. Additionally, biochemical markers of apoptosis including DNA fragmentation and Ley antigen expression were induced in association with the appearance of morphological and biochemical markers of differentiation (ALP). These results suggest that the hypomethylation of DNA is involved in the molecular mechanism of growth inhibition, induction of apoptosis, and differentiation in human pancreatic cancer MIA PaCa-2 cells.