Feather tips from chickens infected with oncogenic or nononcogenic Marek's disease virus (MDV) were individually tested for MDV antigens by the agar-gel-precipitin test to compare antigen contents of feather follicles infected with oncogenic or nononcogenic MDV. There was a significant difference between oncogenic and nononcogenic MDV in the development of MDV antigens in the feather follicle epithelium of infected chickens. Significantly more feather tips from chickens infected with oncogenic MDV were positive for MDV antigens, particularly at 3 and 6 weeks postinoculation, whereas the feather tips from those infected with nononcogenic MDV were rarely positive, whether tested with the homologous or heterologous anti-MDV serum. Such a difference was consistent in separate trials employing three different strains of chickens. Infectious cell-free MDV was extracted more frequently from the feather tips of chickens infected with oncogenic MDV than from those of birds infected with nononcogenic MDV, and the virus titers of extracted MDV were always numerically or statistically higher in birds infected with oncogenic MDV.