109Cadmium was microinjected, in different chemical forms, into the proximal or distal cortical tubules of adult rats and recovery in the pelvic urine from the ipsilateral kidney was measured. There was marked uptake of inorganic cadmium along the proximal tubules, and only negligible uptake in the distal nephron. The fractional uptake of the complex cadmium-cysteine in the proximal tubule was inversely related to the cysteine concentration. The chelate cadmium-pentetic acid was completely recovered in the pelvic urine.