Based on some anecdotal case reports D-penicillamine (DPA) has been advocated for the treatment of arsenic poisoning. Experimental evidence, however, supporting that recommendation is lacking. In the present experiments the effectiveness of DPA was compared with dimercaprol (British Antilewisite, BAL), dimercaptopropanesulfonate (DMPS), and dimercaptosuccinic acid (DMSA) using different controlled experimental settings. In one study mice received As2O3 (9-14 mg/kg sc). Treatment with DMSA after 30 min afforded almost complete protection against the lethal effects of arsenic whereas DPA was not effective. In a second study, mice and guinea pigs were injected sc with 8.4 mg/kg As2O3 (containing a tracer dose of 74As). Thirty min later 0.7 mmol/kg of DPA or one of the other antidotes was injected ip. As determined 4 and 12 h after the arsenic injection, DPA was unable to reduce the 74As content in any of the organs investigated (blood, liver, kidneys, lungs, heart, brain, testes, spleen, skeletal muscle, and skin). On the other hand, BAL, DMPS, and DMSA markedly reduced the tissue content of 74As with respect to controls. Finally, the ability of the antidotes to reverse biochemical effects of arsenic was investigated in vitro using suspensions of incubated renal tubulus cells. The marked inhibition of gluconeogenesis induced by 30 mumol/L As2O3 was almost completely reversed upon addition of 90 mumol of either BAL, DMPS, or DMSA. In this experimental model, too, DPA was ineffective. It was concluded that the use of DPA in arsenic poisoning needs to be reevaluated.