The interactions of citrate reduced colloids (Ag, Au, and Bi) with intact erythrocytes and erythrocyte lysate have been studied by 1H spin echo NMR. Silver colloid is observed to induce cellular depletion of cytosolic glutathione and bismuth colloid induces cytosolic glutathione oxidation in the intact cell. In comparison, there is no detectable effect with gold colloid. With red cell lysate the three colloids all remove glutathione from the spectrum. The metal salts AgNO3 and NaAuCl4 both oxidize intracellular glutathione to diglutathione whereas BiO(NO3) has no effect. Thus colloidal preparations have a different reactivity to their parent metal salts. The differences observed between the three types of colloids (silver, gold, and bismuth) are unique to the colloids studied. None of the colloids studied were biologically inert in the erythrocyte model used.