WITH the technique for polio vaccine production used at present, the end-point titres often are in the neighbourhood of 106/ml., which is recommended as the lowest limit. Different methods have been tested to find a simple way for concentration of the virus. The physical and chemical methods proposed so far are rather complicated and give a comparatively low yield of virus1. Variations in the technique for cultivation of the virus have also been suggested as a means of increasing the virus titres2.