The existence of an autocrine loop for self-stimulation of growth in malignant cells has been proposed for transforming growth factor-alpha (TGF alpha) and its receptor, the epidermal growth factor (EGF) receptor, in a variety of malignant cell types. Expression of both has been described in colon carcinoma. In order to investigate whether there is a correlation between TGF alpha and EGF receptor mRNA expression and differentiation, we studied the effects of differentiating agents on seven human colon carcinoma cell lines. All of the lines responded to the differentiating agents. In four of the seven lines there was increased EGF receptor mRNA two to five days after treatment with 2 mM sodium butyrate. In three of these lines TGF alpha mRNA and protein were also increased. In the one cell line treated with the differentiating agents DMF and DMSO, EGF receptor mRNA was also increased. [125I]-EGF binding to the cells was measured before and after treatment with butyrate. In two of three cell lines, increased EGF receptor mRNA was accompanied by a 2.4-fold increase in the number of binding sites per cell. In SW620 cells, no EGF receptor binding was detected before or after butyrate treatment. In the two cell lines in which butyrate increased EGF receptor binding, simultaneous treatment with EGF did not enhance growth. These data demonstrate increased expression of the TGF alpha/EGF receptor system after differentiation of colon carcinoma cell lines and suggest that their expression may be characteristic of a differentiated phenotype.