Stable hematopoietic chimeras immunized with bacteriophage φX174 have primary and secondary antibody responses with Ig class switching similar to that of control animals. At the time of 1° immunization, animals A89164, A89163, and A91382 were 1,324, 1,212, and 835 days posttranplantation, respectively. (•) Experimental animals; (○) control animals.