We have investigated the presence of oestrogen receptor-related (ERR) mRNA in human colorectal tumour tissues and adjacent normal mucosa by reverse transcriptase and nested-polymerase chain reaction. ERRalpha was found in 100% of the patients and ERRgamma in approximately 30% while ERRbeta was not detected at all. The multiplex PCR analysis showed elevated levels of ERRalpha mRNA in tumour tissue compartment as compared to normal mucosa, whereas ERRgamma mRNA was found in lower levels but in both tissue compartments. In contrast, oestrogen receptor (ERalpha and ERbeta) mRNA levels were shown to be decreased in tumour tissues. A positive correlation was observed between ERalpha and ERbeta and between ERalpha and ERRalpha, respectively, in normal mucosa but not in tumour tissue. ERRalpha expression in tumour tissues significantly increased from TNM stages II to IV, whereas both ERs progressively declined. These findings suggest that ERRalpha, as well as the two ERs, might play a critical role in the progression of the colorectal cancer.