For further understanding the sisafety of the lapinized hog cholera virus (LPC strain; island-widely ernployerl for more than 20 years in Taiwan) and the tissi-culsui virus (OPE-stain; adopted for hog cholera evention in Jaen since 1969) the writers had reverse-ssagal these two hve vaccine viruses respatvely in SPF pigs for 20 essages in order to find the pcxssibihbies of recovery of the virulence, The result were summaril as follows:
1. No pathogenic recovery was detctol when these two stains were respettively passei for 20 serial ssa,ges in SPF pigs. Only a few cases sho slight fever reaction, the others appeared qyite normal.
2. In Uocd examination, slightly treaserl WEC count was found in both earlier passages. Neutrophuls were somewhat increased bothinearlier4 passages of LPC group and at the 6th and 7th passages of GP group.
3. hicculated pigs all showeri virernia negative when examined at the 3rd and 5th day ptin(x),latiOn.
4. In autop€y, only several peechiaes were found in bladders, splns and kidneys in some cases.