Vitamin B-12 status was assessed in a group of 110 adults and 42 children from a macrobiotic community in New England. Dietary and anthropometric information also was obtained. Fifty-one percent of the adults had low concentrations of serum vitamin B-12, which inversely correlated with duration of macrobiotic diet practice. Urinary methylmalonic acid (MMA) excretion was inversely correlated with serum vitamin B-12, and 30% of adults sampled had high urinary MMA. Fifty-five percent of children had high urinary MMA, and MMA was higher in the group that consumed a macrobiotic diet during their entire lifetime. Children were relatively short in stature and weight, and decreased stature was associated with high urinary MMA. In both adults and children vitamin B-12 status was better with more consumption of dairy products or with higher tertile of reported frequencies of vitamin B-12 consumption of various animal products. Vitamin B-12 status appeared to be unrelated to consumption of several vegetarian foods.