Expression of GA733-1 and GA733-2 genes in gastrointestinal tumours was investigated. Twelve cases of colorectal and stomach cancers were analysed. The Northern blot and RT-PCR methods were used. The second method appeared to be much more sensitive and useful in these investigations. No expression of GA733-1 gene was found in the investigated cases. GA733-2 expression was observed in 83% of colon cancers (five to six analysed cases) and in 33% of stomach cancers (two to six analysed cases). No correlation was found between the expression and clinical properties of tumours. Moreover, in two cases the presence of GA733-2 mRNA was observed in the surrounding morphologically normal tissue. These results indicate that GA733-2 gene can be a good marker of colon but not stomach cancers.