Series of attempts were made to adapt the Phylaxia vaccinal strain (Hungary) to various cell cultures in vitro. The work with twenty-one successive passages of the virus in a culture of lamb testis resulted in the production of an adapted strain that could produce a characteristic cytopathic effect at the 24th--48th hour of the infection, reaching a titer of 10(4.5) ID/cm3. Cytologic and electron-microscope investigations confirmed the fact that this cell strain belonged to the Parapoxvirus genus. The experimental infection of 4-5-month-old lambs showed that the virus strain retained its capacity to cause typical clinical signs of infectious ectyma. It could be used in the production of a cell-cultural vaccine.