A controlled vaccination trial was conducted using a commercial Vero cell line origin modified-live canine distemper virus (CDV) vaccine (Galaxy D\sp\circler, Solvay Animal Health, Inc., Kitchener, Ontario, Canada) in 47 racoon pups of known immune status. All CDV antibody-negative pups developed detectable antibody titers within 2 weeks of vaccination. Eight CDV antibody-negative pups vaccinated once at 8 weeks of age and eight CDV antibody-negative pups vaccinated at 8, 12 and 16 weeks of age had similar titers at 20 weeks of age. Antibody-negative racoons first vaccinated at 8 weeks of age mounted titers similar to those of racoons first inoculated at 16 weeks of age. In eight unvaccinated pups, maternal antibody titers waned to negligible levels by 20 weeks of age. The half-life of maternal antibodies was estimated at 10.55 days. When eight racoons with maternal antibodies were vaccinated at 8, 12 and 16 weeks of age, only the third vaccination resulted in increased antibody titers. At 20 weeks of age, pups which initially had maternal antibodies to CDV had lower titers than CDV antibody-negative pups given the same vaccination protocol. When challenged with a virulent racoon-origin CDV that caused clinical disease 29 and 30 days post-inoculation in three out of four controls and lesions of canine distemper (CD) in all four, 16 vaccinated animals showed no clinical signs of distemper over a follow-up period of 42 days and were free of lesions of CD at necropsy. Results of this study suggest that vaccination using this modified-live virus product in racoon pups was safe and efficacious, and yielded protection from clinical disease. A vaccination schedule consisting of serial inoculations at 8, 12, and 16 weeks of age is recommended.