A comparative study of tissue gold levels produced in guinea-pigs after the oral administration of either triethyl-phosphine gold chloride or Myocrisin (sodium aurothiomalate) or after the injection of Myocrisin intramuscularly is reported. Gold concentrations were determined 5, 24 and 168 hours after administration in stomach, small intestine, large intestine, kidney, liver and spleen and 5 and 24 hours after administration in skin, adrenals, heart, lung and brain. In gastrointestinal tissues, tissue gold concentrations were highest with triethylphosphine gold chloride. The stomach gold level 5 hours after oral administration of triethyl-phosphine gold chloride is particularly high and, taken in conjunction with the other gastrointestinal gold levels measured, suggests that a stomach rather than an intestinal absorption mechanism may predominate. A more extensive time-course study on kidney and liver is reported and the possible relationship between tissue concentration and toxicity is discussed.