The deterioration of functional and mental capacity is one of the major problems of the elderly. This deterioration may be caused or worsened by folate deficiency. The aim of this investigation was to analyze the relationship between mental and functional capacities and folate status in a group of 177 elderly Spanish people. Folate deficiency is common in the Spanish population. In this study, 48.6% of the elderly subjects had folate intakes below recommended values (200 microg/day), 34.9% had serum concentrations < 14 nmol/L and 6.6% had <360 nmol/L erythrocyte folate. Subjects took part in a series of tests: Katz' scale of activities of daily living, Lawton's scale of instrumental activities of daily living, Pfeiffer's mental status questionnaire, Folstein's Mini-Mental State Test and the Geriatric Depression scale of Yesavage. The results for Lawton's scale of instrumental activities of daily living were significantly better (indicating greater independence and capacity) when folate intake and serum or erythrocyte folate concentrations were adequate (i.e., folate intake no less than recommended, > or = 14 nmol/L serum folate or > or = 360 nmol/L erythrocyte folate). Subjects with adequate Mini-Mental State Exam results (> or = 28 points) had serum and erythrocyte folate concentrations significantly higher than those with less adequate results (<28 points). Thus, there is evidence to suggest that the folate status of the elderly should be monitored and, if possible, improved.