One-hundred seventy four consecutive patients who underwent curative resection for gastric and colorectal cancer between 1983 and 1985, were studied prospectively to evaluate the roles of sequential CEA, TPA and GICA determinations and independent clinical examinations, in the early diagnosis of resectable recurrences. Sixty-six recurrences (33 from gastric and 33 from colorectal cancer) were detected between 6 and 42 months after primary surgery. In gastric cancer CEA, TPA and GICA showed a sensitivity of 64%, 73%, and 60%, and a specificity of 67%, 65% and 54% respectively. Nine patients (27%) underwent surgical treatment for the recurrent disease, and 4 of them (44.4%) had resectable recurrence, for a total resectability rate of 12%. Out of these four patients, three patients are still living after 12, 36 and 44 months respectively from re-operation without evidence of neoplastic disease. In one of these patients re-operation was performed on the basis of the elevation of the three markers, without any other clinical sign of disease, this patient had a resectable solitary hepatic recurrence. In colorectal cancer CEA, TPA and GICA showed a sensitivity of 73%, 73%, and 49%, and a specificity of 77%, 87%, and 97% respectively. Fourteen patients (42.4%) underwent surgical treatment for the recurrent disease, and 8 of them (57%) showed a resectable recurrence, for a total resectability rate of 24.2%. Six patients are still living after 9, 16, 21, 31, 41 and 53 months respectively from reoperation without evidence of neoplastic disease.(ABSTRACT TRUNCATED AT 250 WORDS)