Zinc and copper concentrations were estimated by atomic absorption spectrophotometry in serum, erythrocytes and scalp hair from inhibitants of northern Nigeria. Other measurements performed were serum caeruloplasnIN total protein, albumin and alkaline phosphatase, and blood haemoglobin and haematocrit. The mean serum zinc was significantly lower in non-elite Nigerians (Hausa rural farmers presenting as blood donors) (105.30 + 7.30 ug/100 ml) than in elite Nigerians (University senior staff) (128.90 + 5.80 ug/100 ml) (Pecause of foetal demand. The raised serum copper in pregnancy may be due to increased erythropoiesis. There was no significant difference in measurements between Nigerians with normal haemoglobin pattern (Hb. AA.) and those individuals with sickle cell trait (Hb. AS.). Patients with sickle cell anaemia (Hb. SS.) were observed to have lower mean serum and hair zinc concentrations than elite Nigerians (P<0.01). The erythrocyte zinc levels did not differ significantly between these two groups. There was no significant difference found in measurements between Hb. SS and non-elite groups, but it is probably true that patients with Hb. SS, were nearer the elite families than non-elite families. Patients with Hb. SS. in Nigeria probably do not have clinically significantly zinc deficiency. An elevated serum copper in Hb. SS, is thought to be the result of increased erythropoietic activity. Patients with leg ulcers but not Hb. S.S., showed comparable serum zinc levels to patients With Hb. SS.. probably due to zinc immobiligation from chronic tissue damage. Significantly decreased serum zinc concentrations have been demonstrated in the following conditions: primary liver cancer, hookworm anaemia, active pulmonary tuberculosis and leukaemias. The serum copper was elevated in these conditions. The pathophysiological mechanisms underlying these changes may be increased urinary excretion and loss of body stores of zinc. These changes in serum zinc and copper may result in part from a redistribution of the metals within the body initiated by a hormone-like protein factor which is released from phagocytic cells. This factor, leukocytic endogenous mediator (LEM), stimulates the liver to take up zinc and iron from serum into the liver and to synthesize additional quantities of caeruloplasmin. This work has established the normal ranges of zinc and copper concentrations in the northern Nigerian population with relation to social class and haemoglobin patterns, and that zinc deficiency is not a common feature in Nigeria. The estimation of trace element concentrations may be a useful means of predicting the health status of various community groups in the general population; and the changes occuring in trace element concentrations may be a useful tool in following the progress of patients with malignant disease during the course of treatment.