Statens Serum Institut has developed a new vero-cell culturing technique for the manufacturing of inactivated poliovirus vaccine (IPV). This technique implies that the cultivation of cells and poliovirus is performed in a medium free of materials of animal origin and free of antibiotics. In a double-blind randomised clinical trial, IPV(vero) manufactured by this new technique was compared to conventionally produced IPV(mkc). One hundred and twenty-nine (129) healthy adult volunteers were given booster vaccinations of IPV(vero) (65) or IPV(mkc) (64). Both vaccines were well tolerated and resulted in excellent booster responses. No statistically significant differences were seen between the study groups.