A leukocyte migration inhibition assay was used to demonstrate antigen-specific cell-mediated immunity (CMI) in chickens vaccinated with the V4 strain of Newcastle disease virus. Chickens were vaccinated when 5 weeks old, and again 3 and 7 weeks later. CMI was detected 9 days after initial vaccination by eyedrop, but only after the second dose of vaccine delivered into the crop. In some chickens there was a temporary suppression of CMI to Newcastle disease virus, especially after the initial application of vaccine to the crop. Haemagglutination inhibition antibodies developed to similar levels in chickens after vaccination by either route. There was no obvious correlation between antibody and CMI responsiveness.