Primary kitten kidney cultures are frequently contaminated with wild feline infectious enteritis (FIE) virus and this led the authors to develop feline embryo diploid cell lines. Monolayer cultures were prepared from the lungs or from eviscerated and decapitated carcases of embryos obtained by Caesarian section from healthy pregnant queens. At about the 30th passage, these cells lost their fibroblastic morphology to become polygonal. After a further thirty passages the monolayers exhibited foci of low cell density circumscribed by bands of cells stacked in disorganized arrangement. All the developed cell lines were susceptible to infection with FIE virus and produced intranuclear changes resembling those described by Johnson (1965) in primary kitten kidney monolayers.

On four occasions the cell lines became contaminated with Mycoplasma and although there was evidence that the virus could infect the cells, there was no production of infective virus.

A simple karyotype was devised in which the 38 chromosomes were arranged in three groups according to the arm-length ratio and the percentage mean index length. After the 50th passage many of the nuclei of lung-derived cultures exhibited abnormal chromosomes resulting from ring formation or translocation, whilst those of embryo culture demonstrated a new modal chromosome number of 37.

We are grateful to Mrs L. Hitchcock and Mrs P. Waller, A.I.S.T., for technical assistance, to Mr E. A. Jones, A.I.I.P., for the photomicrographs and to Dr R. H. Johnson, University of Bristol, for supplying the leopard and mink enteritis viruses.