Serum zinc and C-reactive protein (CRP) levels were measured in two groups of acutely ill geriatric hospital in-patients. Serum CRP levels were greater than 10 mg/l in 62% of the first group and 47% of the second. There was a significant negative correlation between zinc and CRP in both groups (r = -0.33, P less than 0.001, n = 103) and (r = -0.29, P less than 0.001, n = 135 respectively). The serum CRP was raised in 30% of long stay patients (n = 50) and 23% of a control group of elderly hospital patients with a normal serum albumin (n = 71), but there was no correlation between zinc and CRP in these patient groups. The results indicate that an acute phase response influences serum zinc levels in acutely ill geriatric patients. There is reason to believe that a distinction should be made between true zinc deficiency and a low serum zinc secondary to acute zinc redistribution during an inflammatory response. Measurement of CRP may help to distinguish between these two situations. We advise that if the serum zinc is low and CRP is significantly raised, zinc supplements should be avoided and a source of infection should be sought. Following recovery from severe infection low serum zinc levels return to normal while elevated CRP levels fall.