To investigate the relationship between homocysteine (Hcy) and B vitamins status in the Taiwanese elderly population, an analysis was made of the plasma Hcy levels in elderly persons. The study sample was taken from the Elderly Nutrition and Health Survey in Taiwan (1999-2000) (Elderly NAHSIT) and included 1094 males and 1135 females aged 65-90 years. The results showed that average plasma Hcy was 13.3+/-0.6 micromol/ L for males and 10.6+/-0.7 micromol/L for females. The average plasma Hcy levels of males from all age groups were significantly higher than those of females, and significantly increased with age (P<0.0001). The overall prevalence of hyperhomocysteinemia (Hcy>15 micromol/L) was 23.4% for elderly males and 11.2% for elderly females, and this also increased with age (P<0.0001). In subjects with normal renal function, folate, vitamin B2, B6, and B12 status were significantly lower in males with hyperhomocysteinemia, while only folate and vitamin B12 were significantly lower in females with hyperhomocysteinemia. Further analysis suggested that folate, vitamin B6 or B12 insufficiency were associated with hyperhomocysteinemia in both sexes, while vitamin B2 insufficiency was significantly associated only in males. In elderly persons with adequate folate, vitamin B6, and B12 status, there was no significant association between vitamin B2 and hyperhomocysteinemia. This association occurred only in those who had concurrent poor folate, vitamin B6, or B12 status. The strength of the association between vitamin B12 insufficiency and hyperhomocysteinemia was not affected by simultaneous vitamin B2 or B6 insufficiency, but increased about 3-fold when combined with folate. This suggests that poor folate and vitamin B12 status has a synergistic effect on the risk of hyperhomocysteinema in the elderly, as did a poor folate and vitamin B6 status. Therefore, maintaining adequate vitamin B12 status and avoiding multiple B vitamin insufficiency, especially that of folate and vitamin B12 or B6, should be emphasized as an important measure for reducing plasma Hcy levels among elderly Taiwanese.