Six patients with an early stage of gastrointestinal (GI) cancer (T1N0M0, stage I) were successfully treated by photodynamic therapy (PDT) as follows: esophagus-1, stomach-2, rectum-3. The patients were photosensitized 72 hrs prior to treatment with pure hematoporphyrin at a dose of 5.10(-6) kg/kg b.w. in a slow intravenous infusion. Argon-pumped dye laser light at 0.630 microns wavelength was used in single and multiple treatment sessions with the power density ranging from 0.015 to 0.192 W.m-2 and a dose varying from 0.320 to 1.600 kJ.m-2. Tumor eradication (complete response) was obtained in each of the patients. No early or late treatment related complications were recorded. The patients were followed-up in the course of 7-16 months after treatment and no local recurrence or general development of disease (metastases) were reported. PDT in the early stage of GI carcinoma was recognized as a radical therapeutic method in clinical oncology.