Cancer cells with homologous recombination deficiency (HRD) exhibit a distinctive vulnerability to poly(ADP-ribose) polymerase inhibitors (PARPis). To address the limitations of existing methodologies incapable of providing real-time insights into homologous recombination (HR) status, we present an adenovirus-based functional assay designed to quantify cellular HR activity. Here, we delineate the step-by-step procedure for producing the adenovirus harboring an HR reporter, processing primary cells, and assessing HR activity in primary ovarian cancer cells.