Populations of fibroblast-like cells of corneal stroma, heart ventricle, and back skin of day-14 embryonic chicks were grown in vitro as primary and secondary cultures and were found to differ from one another by several criteria. Such cells were obtained from tissues either directly (cornea) by dissection or indirectly (heart and skin) by the rapid adhesion of the fibroblast-like cells to glass and plastic substrata. Individual fibroblast-like cells of cornea and heart were distinguishable from one another during their first 24–48 h in vitro. The morphologies of the individual cels of these 2 populations became indistinguishable during logarithmic growth, although each could be distinguished from individual fibroblast-like cells of skin. When the cultures reached saturation, corneal cells formed a monolayer of randomly oriented polygonal cells; skin cells formed a monolayer of long, narrow, ragged cells in parallel arrays with occasional double-layering; and heart cells formed multilayers of criss-crossed cells whose broad, smooth outlines were in parallel array in each layer. Saturation densities of the 3 fibroblast-like populations were different: heart greater than skin greater than cornea. By 3 methods of assay the cells were found to be differentially sensitive to treatment with trypsin and EDTA, and to EDTA alone, heart cells consistently being the least sensitive. Taken together, these data suggest that fibroblast-like cell populations isolated from different tissues of a single organism are different from one another and thus may behave differently from one another during in vitro studies.

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