The aim of the study was to determine the influence of simultaneous infection of chicken embryo fibroblasts (CEF) with different doses of adenovirus field strain serotype 7 (FAdV-7 JN-5/10j) and turkey herpesvirus strain FC126 (FC126 HVT) on replication of the herpesvirus in in vitro cultures. Three experiments were performed: simultaneous infection of CEF with adenovirus and HVT; inoculation of CEF culture with adenovirus, followed by infection with HVT after 24 h; and inoculation of CEF with HVT, followed by the infection with adenovirus 24 h later. In order to detect the presence of HVT and adenovirus strains in CEF culture, SORF 1 and hexon genes were determined, respectively. The infection with adenovirus lowered replication of FC126 HVT in chicken embryo fibroblast.