Single and paired control Novikoff and connexin 43 antisense-transfected Novikoff cells (antisense cells) were used to investigate the differences of intercellular dye transfer and leakage between these two types of cells. Lucifer Yellow was injected into cells by iontophoresis. There was no dye leakage in single cells of both types in Swims solution. The dye transfer from injected cell to recipient cell in the normal solution was different in the two types of cell pairs. The transfer was significantly suppressed in antisense cells; 46/84 cases were blocked vs. 1/84 in Novikoff cell pairs. Under EGTA treatment, the dye leakage in single antisense cells was suppressed showing an increase in the very slow rate of leakage (16/40 vs. 6/40), and the mean rate of leakage was also significantly low. This suggests that dye transfer and leakage are suppressed in antisense cells and demonstrates that connexin 43 plays an important part both in dye transfer in paired cells and dye leakage in single cells.