It has recently been published the results of a prospective, comparative study for adjuvant chemotherapy of 164 colorectal cancer patients. Pathological stages were Dukes B 79, C 85 of the cases. The site of primary tumour was colon 108, rectum 56 of the patients. The treatment protocols were as follows: 425 mg/m2 5-fluorouracil plus 20 mg/m2 leucovorin on days 1-5 at 28 days cycles six times (LV group). The IFN group received the same chemotherapy completed with weekly 3 x 3 MIU interferon alpha. Both treatment groups were well balanced. The mean follow up time was 38.1 months. There were 91 patients of relapse and 65 deaths this time. The time to progression was 15 months in the LV group and 12.7 months in the IFN group (p < 0.05). The mean survival time was 24 months in the LV group compared to 22.3 of the IFN group. The frequency and sites of relapses did not differ statistically between the both groups. The preoperative CEA-level was elevated in 42 cases. The mean survival time was 26.4 months in the cases having normal CEA-level compared to 16.1 months of the cases with high-level (p < 0.001). The side-effects were transient and mild, while in the group treated with interferon were more instances of fever, fatigue, flu-like syndrome, psychic disorders, depression and agitation. The administration of interferon had to be interrupted in 4 cases. The results of interim analysis suggest choosing the so-called Mayo protocol for the standard adjuvant treatment of colorectal cancer.