The development of a heat-stable poliovaccine preparation is urgently needed for the eradication of polio in tropical countries. In the present study, in order to obtain heat-stable lyophilized poliovaccine (type 1, 2 and 3 Sabin strains), conditions affecting the lyophilization of the vaccine viruses were studied. With regard to lyophilizing medium (medium used for suspending virus before lyophilization), the effect of a single chemical component, and double and tripple chemical components on lyophilization and subsequent incubation at 37℃ or 45℃ was examined stepwise. The composition of reconstituting medium (medium used for suspending the lyophilized virus) was also examined in a similar manner. The results suggested excellent effects of a combined medium consisting of 2.5% sorbitol, 0.06%-0.1% glutamine (or arginine) and 0.01% BSA for lyophilization and a medium composed of 5%-10% polypeptone S and 10%-15% sucrose for reconstitution. An attempt to select a vaccine virus variant which is resistant to lyophilization by means of repeated lyophilization followed by multiplication in cell cultures was unsuccessful.