Introduction - Poisoning due to lead and its compounds has short and long-term effects primarily on the nervous, hematopoietic, gastrointestinal, cardiovascular, musculoskeletal, renal and reproductive systems. It can manifest in acute or chronic symptoms. Measuring serum concentration is the primary method for diagnosing and monitoring exposed workers. Presently, elevated lead levels are treated by drugs whose effectiveness is contested on various fronts. Experimental studies suggest that homeopathic preparations may be in controlling blood lead levels in laboratory animals, creating the need for controlled studies to evaluate the effectiveness and safety of these preparations in humans.Objective - To evaluate the effectiveness of the homeopathic preparation Plumbum metallicum in reducing the blood lead level of workers exposed to this metal.Design - Double-blind randomized trial.Setting - Workers’ clinic in the Ajax battery plant, which employs 900 workers with varying degrees of lead exposure in Bauru, São Paulo State, Brazil.Subjects - 131 workers exposed to lead.Intervention - Plumbum metallicum 15cH or placebo, orally for 35 days.Results - The percentage of workers who demonstrated a reduction in lead counts by a percentage greater than or equal to 25% following treatment was the same for both groups: 20.3% in the homeopathic groups versus 21% in the control group [Relative Risk (RR) = 0.95, confidential interval (CI) 95%: 0.47–1.92)]. Analysis by intention-to-treat also did not show any difference between the groups: 18.2% in the treated group versus 20% in the placebo group (RR = 0.91, CI 95%: 0.45–1.84).Conclusion - The homeopathic preparation Plumbum metallicum had no effect, in this study, in terms of reducing serum lead in workers exposed to lead.