Replication-deficient adenovirus (Ad) vectors provide an efficient technology for direct DNA delivery to cells both in vitro and in vivo. We have inserted the measles virus nucleoprotein (N) gene under the control of the strong constitutive CMV major IE promoter into an Ad type 5 E1- vector to produce the recombinant virus RAd68. Following infection of human fibroblasts with RAd68 in vitro, recombinant N protein was synthesized as a 60-kDa protein that represented up to 20% total soluble cell protein. Long filamentous structures were produced in both the nucleus and the cytoplasm that were similar in appearance to measles virus nucleocapsids. These "nucleocapsid-like" structures were readily purified by density gradient centrifugation. Murine immunization with RAd68 elicited (i) a humoral immune response to N, (ii) a major histocompatibility complex class I-restricted, antigen-specific cytotoxic T cell response, and (iii) protection against challenge with the measles virus CAM/RB strain in mice. This study demonstrates the capacity of replication-deficient Ad recombinants both to induce and to characterize cell-mediated immune responses.