The use of cell cultures as a model system for studying thyroid diseases requires establishment of appropriate culture conditions that allow in vitro propagation of populations that correspond to in vivo ones. We have defined these conditions and verified functional parameters such as thyrotropin-dependent cyclic adenosine monophosphate (cAMP) production and thymidine incorporation, and molecular markers such as thyroglobulin (by radioimmunoassay [RIA] and Northern blot), thyroperoxidase (by Northern blot), thyroid-specific transcription factor 1 (by immunohistochemistry and Northern blot) and PAX-8 (by Northern blot). The "in vitro profile" (functional parameters and molecular markers) was found to correlate with the degree of differentiation of the starting specimens and the pathological diagnosis. The data presented suggest that our culture technique allows in vitro growth of cell populations that may be used to perform functional assays and may facilitate the molecular characterization of pathological samples. This approach could be especially useful to define prognosis and also help to develop innovative therapies.