Previous studies in this laboratory have demonstrated that BrdU induces differentiation in the lung epithelial cell lines DLKP (derived from a poorly differentiated carcinoma of the lung) and A549 (derived from an adenocarcinoma of the lung). This differentiation involves the induction of epithelial specific proteins, e.g. cytokeratins-8 and -18, and epithelial related adhesion molecules e.g. (X2P1 integrin. This thesis investigated the effects BrdU has on the expression of Ep-CAM, a non-calcium dependent, homophilic cell-cell adhesion protein, in these cell lines. BrdU treatment induced Ep-CAM protein expression in DLKP after 7 days, with this induction reaching a plateau after 14 days of 10(iM BrdU treatment. Similarly, in A549, Ep-CAM was induced following 7 days of BrdU treatment and the level of induction also plateaued after 14 days of exposure to 10(.iM BrdU. RT-PCR analysis revealed that the effect of BrdU on Ep-CAM expression appears to be at the post-transcriptional/translational level, with no increase in mRNA levels compared to significant increase in protein levels in both cell lines. Ep-CAM is believed to interfere with the functioning of the Ca2+-dependent cell-cell adhesion molecule E-cadherin, by causing alterations in focal adhesion proteins. Analysis of two these proteins, a-actinin and a-catenin, showed that BrdU down-regulated their expression following Ep-CAM induction. RT-PCR analysis of the Ep-CAM homologue GA733-1 revealed that, following BrdU treatment, mRNA expression is induced in DLKP. However, no induction is observed in A549. The ability of other halogenated thymidine analogues to induce differentiation was also investigated. Three halogenated thymidine analogues were selected, each possessing a different mechanism of biological activity, CdU (which incorporates into DNA), 5,5'- FdU (which inhibits DNA synthesis) and 5-BUr (which incorporates into RNA). The ability of CdU to induce the expression of cytokeratin-8, cytokeratin-18, cytokeratin-19, Ep-CAM and (31 -integrin was demonstrated in both A549 and DLKP. RT-PCR analysis of A549 revealed that although the protein expression was induced, the mRNA level remained unchanged indicating that CdU was altering expression at a posttranscriptional/ translational level. A significant up-regulation of cytokeratin-8, cytokeratin-18, cytokeratin-19, Ep-CAM and |31 integrin also occurred in DLKP and A549 following 5,5'-FdU treatment. Analysis of mRNA levels following treatment with 5,5'-FdU indicated that expression was being altered at a post-transcriptional/translational level. Treatment of DLKP and A549 with 5-BUr did not produce any obvious alterations in protein expression or mRNA levels. To develop models reflecting in vivo differentiation, DLKP and A549 were grown in a hormone supplemented medium (HSM) which contained a number of physiologically relevant factors e.g. oestrogen and insulin. Growth in this medium induced expression of cytokeratin-8, cytokeratin-18, cytokeratin-19, and Ep-CAM in DLKP and A549. Experiments to identify the importance o f specific components in HSM revealed that the deletion of hydrocortisone, and cholera toxin from HSM cause an increase in induction of cytokeratin-19 and Ep-CAM. In contrast the removal of insulin from HSM, reduced the ability to induce expression of cytokeratin-19 and Ep-CAM in A549. To further develop in vitro models reflecting in vivo differentiation, methods were established to generate primary cultures of lung tumour cells and normal lung epithelial cells. The assessment of a variety of methods for the isolation of lung carcinoma cells from lung tumour samples did not reveal any advantages between the methods. Preliminary studies on isolated normal rat type II pneumocytes revealed morphological and antigenic changes during in vitro cultivation. These changes were consistent with the terminal differentiation of type II pneumocytes into type I pneumocytes. During the isolation of lung tumour cells cultures of fibroblasts were often established and these expressed the unusual feature of cytokeratin protein expression, which is usually epithelial- specific.