In a reexamination of congenital infection of chickens with ALV, one of the classical models of immunologic tolerance, we were unable to demonstrate that there was any evidence suggesting humoral immune reactivity to the infecting virus. In ALV-F42 congenitally infected birds that have a persistent viremia and no neutralizing antibody detectable by conventional means, we could find no evidence of host IgG deposits in the kidneys, nor any suggestion of renal pathology, or damage. In addition, attempts to precipitate any putative circulating infections virus-antibody complexes by treatment with a highly specific anti-globulin were negative nor were there titer differences in the viremic plasmas of bursectomized birds compared to nonbursectomized birds, indicating that the chickens were not making either a masked neutralizing or a nonneutralizing antibody response to the infecting virus. The evidence presented indicates that congenital infection of chickens with ALV does, at least at the humoral level, result in a state of immunologic tolerance to the infecting agent.