Because of the unavailability of satisfactory tissue culture lines from cetacean species, isolation of viruses from clinical samples from cetaceans and other marine mammals and characterization of these virus isolates has been dependent on non-cetacean cell lines. This laboratory has developed and begun characterization of cell culture lines from several cetacean species. Cell lines derived from beluga whale (Delphinapterus leucas) tissue include a line derived from the testis, designated DeLeuT, and a line derived from brain tissue, designated DeLeuBr. Cell lines derived from the pantropical spotted dolphin (Stenella attenuata) include a line derived from the lung, designated StAttLu, and a line derived from the skin, designated StAttSk. The lines are presently in passages ranging from 30–47 and are maintained on L-15 basal medium supplemented with 10% fetal bovine serum plus MEM nonessential amino acids, BME vitamins, L-glutamine, gentamicin, and antibiotic/antimycotic mix. The lines have not yet been “immortalized” and remain as diploid cultures. They can readily be subcultured at split ratios from 1/2 to 1/10. The lines have to date been tested for susceptibility to one virus of marine mammal origin, specifically the seal herpesvirus (SEHV). All lines proved to be susceptible to SEHV, with cytopathic effect (CPE) being produced most rapidly and most extensively in the lines from Stenella attenuata. The CPE produced consisted of focal lesions in the monolayer having the appearance of grape-like clusters. A similar CPE has been reported in other mammalian cell lines susceptible to SEHV (e.g., Vero). The lines have also demonstrated broad susceptibility to human viruses representing the viral families of Herpesviridae, Poxviridae, Rhabdoviridae, Picornaviridae, Paramyxoviridae, Reoviridae, Togaviridae, and Bunyaviridae. Specific viruses tested included herpes simplex virus-1, vaccinia virus, vesicular stomatitis virus, echovirus-11, subacute sclerosing panencephalitis virus, measles virus, respiratory syncytial virus, parainfluenza virus-3, and reovirus-3. The broad viral susceptibilities of the four cell lines are a favorable indication of their potential for use as viral diagnostic tools for marine mammals.