Serum calcium, magnesium, iron, copper and zinc were measured in 117 patients with cystic fibrosis. Apart from serum iron levels, all the other essential element levels were well maintained and there was no evidence of a need for supplementation. Serum iron was frequently low and the need for iron supplements must be considered after further investigation. The subjects studied covered a wide age range, had widely varying fat malabsorption and clinical grading, and also varying degrees of pulmonary involvement. We found no evidence that any of these parameters directly influenced essential element status as assessed by serum levels.