From March 1992 until January 1994, 1,014 patients radically resected for Dukes' B(2), B(3) or C colon cancer were randomized to receive FU plus levamisole or FU plus leucovorin (LV) plus levamisole. Only 41% of patients older than age 70 years, as compared to 53% of those younger, have completed the treatment as planned. This poorer compliance was not associated with a higher incidence or degree of toxicity. Only a small difference in percentages was detected between the age groups of patients requiring dose reductions or treatment delays, while the percentages of patients that had their treatment discontinued was markedly increased in the older age group, without a parallel increase in severe toxicity. Preliminary results suggest that adjuvant chemotherapy with FU plus levamisole or FU plus LV plus levamisole is well tolerated by elderly patients and is not associated with greater toxicity in patients over 70 years of age than in younger patients. The lower adherence to the treatment plans in older patients may be due to reluctance by physicians and families to administer chemotherapy due to the misconception that the elderly are more prone to adverse reactions.