Recombinant adenoviruses expressing human BRCA1 (AdBRCA1), murine Brca1 (AdBrca1), three clinically relevant human mutant BRCA1 proteins (t340, C61G, and 1853Stop), or a murine Brca1 C-terminal deletion mutant were constructed and evaluated in vitro. These recombinants were capable of transducing high-level transgene expression to a wide variety of cell lines in vitro. Three independent methods were utilized to monitor cell growth following transduction with these recombinants. High-level expression of either the human or mouse wild-type BRCA1 protein was incompatible with maximal levels of cell growth. AdBRCA1 transduction inhibited the outgrowth of several human breast and ovarian cell lines in colony formation assays. Flow cytometric analysis revealed an accumulation of the transduced cells in the G0/G1 phase of the cell cycle. This BRCA1-mediated accumulation of cells in G0/G1 was accompanied by an increase in the cellular level of hypophosphorylated pRB. Ad mutant BRCA1 t340, C61G, and 1853Stop viruses were impaired, to varying degrees, in their ability to transduce a growth-arrested state to the target cells. Using these same three criteria, overexpression of murine Brca1 by AdBrca1 was also capable of transducing a growth-arrested state to human cells. Deletion of the C-terminus of Brca1 diminished this activity. This panel of adenoviruses may be useful reagents as part of an approach to understand the function of BRCA1/Brca1 in normal breast and ovary and help to define the tumor suppressor defect (s) conferred by clinical BRCA1 mutations in breast and ovarian cell tumorigenesis.