The CD38 gene encodes a membrane-bound protein that takes part in cell adhesion and catalyzes the formation of cyclic ADP-ribose. The presence of the full-size and alternative forms of CD38 mRNA in tumor tissue specimens from patients with colorectal cancer and tumor cell lines was analyzed by RT-PCR. It was shown that tumor specimens contained cells that constantly express CD38; full-size CD38 mRNA was detected more frequently than its alternative form. CD38 mRNA was found in Colo-205, T-84, HCT15, and HCT116 cells, but not in Caco-2 or SW-620 cells. CD38 expression was observed in all cases of stage-I colorectal cancer; at stages II, III, and IV, it was significantly less frequent. The frequency of CD38 mRNA detection did not depend on the localization or grade of the tumor, or the presence of metastases. An analysis using meth- ylation-sensitive restriction endonucleases showed that CpG dinucleotides were methylated at the binding sites of the Sp1 transcription factor and retinoic acid receptor in all tumor specimens studied, regardless of the presence or absence of CD38 mRNA. The obtained data suggest that CD38 expression in tumor cells of colorectal cancer patients is heterogeneous.