Antisera to the MHV-S, -A59, -JHM, and -Nu67 (20) strains were prepared from 7-week-old female ICR mice inoculated oronasally with 1 ϫ 10 6 to 1 ϫ 10 7 50% tissue culture infective doses (TCID 50 )/100 l of MHV culture stock.