The serum levels of copper and zinc were estimated by atomic absorption spectrometry in 7 women with silastic implants releasing norethisterone acetate 140 μg/day. No appreciable change was observed in the circulating concentrations of either of the trace metals after use of the implant for a period of up to 12 months. There was also no change in the serum copper and zinc concentrations during the proliferative and secretory phases of the normal menstrual cycles in 15 women.