A relation between serum zinc level and susceptibility to infection in older inpatients has not been studied well. A relation between serum zinc level and susceptibility to infection in older adults with long-term hospitalizations was studied. Forty-four(13 men, 31 women)hospitalized patients aged 45 years and older(mean, 81.4 years; range, 45-98 years with 38 patients(86%)aged 65 years and older)were divided into two groups. Retrospectively, 22 were assigned to the "no-infection group," with 22 assigned to the "infection group." Patients in the "no-infection group" did not receive any intravenous antibiotic treatment for bacterial infection for six months, whereas the others received at least one such treatment in the past six months. Serum concentrations of zinc, copper, albumin, total cholesterol, glucose, hemoglobin, and c-reactive protein were measured by general methods after six months observation. Mean serum Zn level was 56.9 μg/dL(SD, 14.4)in the "no-infection group" and 47.7 μg/dl(SD,14.9)in the "infection group." Difference in levels was significant(P=.043). Serum levels of albumin, total cholesterol, and hemoglobin in the "no-infection group" were also significantly higher than those in the "infection group." Deficiency in serum zinc appears to be associated with susceptibility to infection among older patients with long-term hospitalizations.