The 293A cell line efficiently produces, amplifies, and titrates replication-incompetent adenovirus. Its flat morphology simplifies titration. The cells contain a stably integrated E1 gene, which enables the expression of the E1 proteins (E1a and E1b) needed to make recombinant adenoviruses. These capabilities allow researchers to screen and develop adenoviral constructs more accurately than ever. The 293A cell line is an essential tool for producing high-quality viral preparations.