Clone (cl.) 85 infection of 15I5 x 72 chickens at 4 weeks posthatch results in a lower frequency of distal sarcomas than does Prague (Pr)-B infection. As higher titers of virus-neutralizing antibody are generated in the cl.85-infected chickens, the possibility was addressed in the present study that the low frequency of cl.85-induced distal sarcomas is a direct consequence of the strong neutralizing response. Our observations indicate that ablation of humoral immunity by embryonic bursectomy does not serve to increase this frequency, implying that the antiviral humoral response is not required to limit formation of cl.85-induced distal sarcomas.