The influence of chronic iron deficiency anaemia on myoglobin content, maximal enzyme activities and capillarization in the human skeletal muscle was investigated. Muscle samples from musculus vastus lateralis were screened in an Indonesian population. The causes of iron deficiency were chronic intestinal bleeding or repeated pregnancy combined with low iron intake. The maximal activities of iron-dependent and non-iron-dependent glycolytic and oxidative enzymes as well as myoglobin showed similar values in the iron-deficient group and the matched control group. The activities of the oxidative enzymes in both the iron-deficient group and the controls were lower, however, compared even to untrained Swedish subjects. The capillary density was essentially within a normal range in both groups. It is concluded that chronic iron deficiency anaemia of a moderate or severe degree, with Hb concentrations of about 80-100 g.1(-1), does not cause an impaired biochemical function of the human skeletal muscle.