The growth of canine parvovirus (CPV) in Crandell feline kidney cells was suppressed when canine distemper virus (CDV) was simultaneously inoculated. The both virus antigens were found in the same cells. The synthesis of capsid protein antigen of CPV decreased in the co-inoculated cells. The growth of CDV was not affected by co-inoculation with CPV. These results suggest that the CDV showed suppressive effects on the CPV growth in cells when they are inoculated simultaneously.