The Gastrointestinal Tumor Study Group, a multispecialty collaborative clinical research program, executed two studies of surgically resected colon carcinoma, including patients with serosal penetration but no positive regional lymph nodes (stage B2). In the first study, 232 patients with stage B2 disease were operated on and survival was unaffected by therapy. In the stage B2 group, survival was 78% at five years, and is estimated to be 64% ten years after surgery. A second study, begun in 1979, compared survival and recurrence data on patients who underwent surgical resection and were treated postoperatively with fluorouracil and hepatic irradiation vs those who were observed. Hematologic toxicity of the regimen and accumulation of data from the first study caused the termination of randomization of patients with stage B2 disease with continued registration to observation only. One hundred twenty-four untreated patients with stage B2 carcinoma had a five-year survival rate of 77%, confirming the relatively high survival of this group of patients who are treated with surgery alone. Our patients' five-year survival of 78% corresponds favorably to the 87% survival rate anticipated in an age-, sex-, and race-matched cohort of Americans not specifically diagnosed as having cancer. Adjuvant trials, in seeking improved survival, should recognize that our review of 356 patients implies a considerably higher-than-anticipated five-year survival for the patient with stage B2 disease who undergoes surgical resection.(ABSTRACT TRUNCATED AT 250 WORDS)