The epidermal growth factor receptor (EGFR) was investigated by an enzyme immunoassay in neoplastic tissue and surrounding mucosa from 43 patients with colorectal cancer. This study found a positivity of 86% in normal samples and a positivity of 93% in neoplastic ones. In normal tissue samples, EGFR levels were 162 +/- 129 ng Ab B/mg protein, while in colorectal neoplastic samples EGFR levels were 228 +/- 135 ng Ab B/mg protein. This difference was statistically significant (p < 0.01). There was a significant correlation between the EGFR levels in neoplastic tissue and those in surrounding mucosa (r = 0.75). In 5 of 43 patients, the EGFR was evaluated also by Western blotting with three different anti-EGFR antibodies, of which one was biotin-conjugated. The presence of a 170-kDa band was detected. Moreover, by using the anti-EGFR mAb biotin conjugate a 90-kDa band was also detected.