[Detection of leukosis on brown Leghorn chicken farms].

Samples taken on the Brown Leghorn hen farms were tested for the leucosis virus. Out of 21 samples the leucosis virus was present in five cases (24%). Viruses are detectable in chicken embryonic cells, accompanied by transformation and focus formation. Viruses are not transformed by the guniea pig and quail embryonic cells. The results were achieved by fusion but not by co-cultivation of the tested cells with permanent line 16 Q. These viruses appear to belong to the sub-group B, it is less probable that they belong to the sub-group C. The isolated viruses document spontaneous infection of the originally leucosis-free hen farm during five years when leucosis-free conditions were not secured.